Move guassopt to optics/guassopt

This is a PR to move ```sympy.physics.guassopt``` to ```sympy.physics.optics.guassopt```.
I tested it on my machine and it works. I.e. previously this fails:
```
ondrej@kittiwake:~/repos/sympy((ad4c101...))$ bin/doctest sympy/physics/
============================= test process starts ==============================
executable:         /usr/bin/python  (2.7.3-final-0) [CPython]
architecture:       64-bit
cache:              yes
ground types:       python 
hash randomization: on (PYTHONHASHSEED=1009248989)

sympy/physics/paulialgebra.py[4] ....                                       [OK]
sympy/physics/qho_1d.py[2] ..                                               [OK]
sympy/physics/units.py[3] ...                                               [OK]
sympy/physics/pring.py[2] ..                                                [OK]
sympy/physics/sho.py[2] ..                                                  [OK]
sympy/physics/matrices.py[4] ....                                           [OK]
sympy/physics/secondquant.py[59] ...............................................
............                                                                [OK]
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "sympy/utilities/runtests.py", line 649, in _doctest
    failed = not t.test()
  File "sympy/utilities/runtests.py", line 1126, in test
    self.test_file(f)
  File "sympy/utilities/runtests.py", line 1149, in test_file
    module = pdoctest._normalize_module(module)
  File "/usr/lib/python2.7/doctest.py", line 203, in _normalize_module
    return __import__(module, globals(), locals(), ["*"])
  File "sympy/physics/gaussopt.py", line 11, in <module>
    deprecated_since_version="0.7.6", issue=7659).warn()
  File "sympy/utilities/exceptions.py", line 154, in warn
    warnings.warn(see_above, SymPyDeprecationWarning, stacklevel=stacklevel)
sympy.utilities.exceptions.SymPyDeprecationWarning: 

Module sympy.physics.gaussopt has been deprecated since SymPy 0.7.6.
Use sympy.physics.optics.gaussopt instead. See
https://github.com/sympy/sympy/issues/7659 for more info.
```
and now it works:
```
ondrej@kittiwake:~/repos/sympy((ad4c101...))$ bin/doctest sympy/physics/
============================= test process starts ==============================
executable:         /usr/bin/python  (2.7.3-final-0) [CPython]
architecture:       64-bit
cache:              yes
ground types:       python 
hash randomization: on (PYTHONHASHSEED=2236610338)

sympy/physics/paulialgebra.py[4] ....                                       [OK]
sympy/physics/qho_1d.py[2] ..                                               [OK]
sympy/physics/units.py[3] ...                                               [OK]
sympy/physics/pring.py[2] ..                                                [OK]
sympy/physics/sho.py[2] ..                                                  [OK]
sympy/physics/matrices.py[4] ....                                           [OK]
sympy/physics/secondquant.py[59] ...............................................
............                                                                [OK]
sympy/physics/wigner.py[6] ......                                           [OK]
sympy/physics/hydrogen.py[3] ...                                            [OK]
sympy/physics/quantum/fermion.py[1] .                                       [OK]
sympy/physics/quantum/anticommutator.py[1] .                                [OK]
sympy/physics/quantum/qexpr.py[2] ..                                        [OK]
sympy/physics/quantum/operatorordering.py[2] ..                             [OK]
sympy/physics/quantum/grover.py[4] ....                                     [OK]
sympy/physics/quantum/tensorproduct.py[3] ...                               [OK]
sympy/physics/quantum/represent.py[6] ......                                [OK]
sympy/physics/quantum/boson.py[1] .                                         [OK]
sympy/physics/quantum/operatorset.py[2] ..                                  [OK]
sympy/physics/quantum/commutator.py[1] .                                    [OK]
sympy/physics/quantum/density.py[9] .........                               [OK]
sympy/physics/quantum/circuitutils.py[3] ...                                [OK]
sympy/physics/quantum/qasm.py[6] ......                                     [OK]
sympy/physics/quantum/identitysearch.py[10] ..........                      [OK]
sympy/physics/quantum/state.py[12] ............                             [OK]
sympy/physics/quantum/qubit.py[5] .....                                     [OK]
sympy/physics/quantum/matrixutils.py[1] .                                   [OK]
sympy/physics/quantum/dagger.py[1] .                                        [OK]
sympy/physics/quantum/circuitplot.py[2] ..                                  [OK]
sympy/physics/quantum/cg.py[3] ...                                          [OK]
sympy/physics/quantum/sho1d.py[6] ......                                    [OK]
sympy/physics/quantum/gate.py[2] ..                                         [OK]
sympy/physics/quantum/operator.py[9] .........                              [OK]
sympy/physics/quantum/spin.py[8] ........                                   [OK]
sympy/physics/quantum/constants.py[1] .                                     [OK]
sympy/physics/quantum/innerproduct.py[1] .                                  [OK]
sympy/physics/quantum/hilbert.py[7] .......                                 [OK]
sympy/physics/mechanics/functions.py[8] ........                            [OK]
sympy/physics/mechanics/lagrange.py[1] .                                    [OK]
sympy/physics/mechanics/rigidbody.py[6] ......                              [OK]
sympy/physics/mechanics/particle.py[6] ......                               [OK]
sympy/physics/mechanics/kane.py[1] .                                        [OK]
sympy/physics/vector/functions.py[9] .........                              [OK]
sympy/physics/vector/frame.py[10] ..........                                [OK]
sympy/physics/vector/printing.py[4] ....                                    [OK]
sympy/physics/vector/dyadic.py[9] .........                                 [OK]
sympy/physics/vector/point.py[11] ...........                               [OK]
sympy/physics/vector/fieldfunctions.py[7] .......                           [OK]
sympy/physics/vector/vector.py[13] .............                            [OK]
sympy/physics/optics/waves.py[9] .........                                  [OK]
sympy/physics/optics/medium.py[6] ......                                    [OK]
sympy/physics/optics/gaussopt.py[28] ............................           [OK]
sympy/physics/hep/gamma_matrices.py[7] .......                              [OK]

================= tests finished: 329 passed, in 17.73 seconds =================
```