Move source to MTpy package folder

This moves source files into the right folder structure for a package named
MTpy, and subpackages MTpy.core, MTpy.imaging, and MTpy.utils.

Note that because the __init__.py files are empty, all modules need to be
imported explicitly for use:

    >>> import MTpy
    >>> dir(MTpy)
    ['__builtins__', '__doc__', '__file__', '__name__', '__package__', '__path__']
    >>> import MTpy.core
    >>> dir(MTpy.core)
    ['__builtins__', '__doc__', '__file__', '__name__', '__package__', '__path__']
    >>> import MTpy.core.OCCAMTools
    >>> dir(MTpy.core)
    ['OCCAMTools',
     '__builtins__',
     '__doc__',
     '__file__',
     '__name__',
     '__package__',
     '__path__']
    >>> import MTpy.core.WS3DTools
    >>> import MTpy.core.BIRRPTools
    >>> dir(MTpy.core)
    ['BIRRPTools',
     'MTtools',
     'OCCAMTools',
     'WS3DTools',
     '__builtins__',
     '__doc__',
     '__file__',
     '__name__',
     '__package__',
     '__path__']

Note that MTpy.core.MTtools was imported indirectly.

Future changes
--------------

We could change this import style in the future so that a select number
of functions and classes were imported into the MTpy namespace, by putting
something like the following in MTpy\__init__.py:

    __all__ = ['some_func', 'some_other_func']
    from MTpy.core.MTtools.some_func
    from MTpy.imaging.ptplots.some_other_func

Then the following would work:

    >>> import MTpy
    >>> dir(MTpy)
    ['some_func',
     'some_other_func',
     '__builtins__',
     '__doc__',
     '__file__',
     '__name__',
     '__package__',
     '__path__']

Or into the global namespace (although this style seems frowned-upon):

    >>> from MTpy import *
    >>> globals().keys()
    [...,
     'some_func',
     'some_other_func',
     ...]

This is the way that many projects are organized, like NumPy and matplotlib.
It has the advantage of keeping code well-organized, but making it accessible
without typing very long module names and paths.
Remove dash from wsmt-pv.py

The dash needs to be removed because the "entry_points" argument in the
setuptools setup function requires scripts to be importable Python
modules, and dashes are not allowed in such module names.

The advantages of using setuptools entry_points, when it's installed,
are such that I think we should forgo dashes in module names.
Fix broken imports

The following files had broken imports from subpackages:

    * MTpy/core/MTPlotTools.py

      Incorrect import of LatLongUTMConversion. Fixed.

    * MTpy/imaging/ptplots.py

      Incorrect import of Z. Fixed.
Add package setup script

Adds a script in the top directory to install MTpy as a Python
package.

Operation
---------

The script caters for two installation scenarios, but is made
so there is no duplication of hand-maintained information.

Scenario A: setuptools is installed. Then the script uses the
"entry_points" argument to setup(). This allows two things: creating
a console script which points to a function within a module, rather
than a whole script; and it wraps scripts in a EXE file on Windows,
making them discoverable by the shell on the PATH variable, making
Tab-completing their names possible.

Scenario B: only distutils is installed. Then only scripts are
available, and they are copied over to the system scripts folder.
Also, distutils does not automatically discover all sub-packages,
so they must be listed.

Maintenance
-----------

There are two parts in this file which need to be maintained by hand:

1. A list of console scripts. This is specified in the "entry_points"
   format, and automatically corrected for distutils if necessary.

2. A list of sub-packages (e.g. 'MTpy.core', 'MTpy.imaging').

Usage
-----

To install the package, if you have setuptools installed:

    $ python setup.py develop

This will install the code in your system site-packages as links to
the original source, meaning that changes will be reflected on reload()
commands.

Or otherwise:

    $ python setup.py install

will copy the source files over to site-packages.

Future changes
--------------

If we release MTpy on PyPi (and I think we should, once it's more
developed), we will need to put metadata arguments in the setup()
function call here, as outlined here:

http://docs.python.org/distutils/setupscript.html#additional-meta-data
http://docs.python.org/distutils/packageindex.html
Add installation instructions to README

Adds "Installation" section with simple instructions for installing
MTpy as a package.
Merge pull request #4 from geophysics/setup_package2

Set up MTpy as a package