Add easier ipython notebook formatting

This commit allows for more "native" display in ipython notebooks.  It won't interfere with anything else; only the ipython notebook will care about the `_repr_latex_` functions.  With these changes, I can simply do something like the following, and get nice latex output in the notebook:
```python
from sympy import *
import sympy.GA
import sympy.GA.ga
init_printing()
coords = (x,y,z) = symbols('x,y,z',real=True)
(o3d,ex,ey,ez) = sympy.GA.ga.Ga.build('e_x e_y e_z',g=[1,1,1],coords=coords)
ex + 3*ey^ez
```

Note, in particular, that I didn't have to use `Fmt`; the last line alone returns the `ex+3*ey^ez` object, which gets printed automatically with mathjax (latex), using the `_repr_latex_` function I've added to `mv` objects.

This PR uses code very close to @lukeburns 's PR #4, but hopefully won't conflict with it.  Either way, his should probably be made first because this is a simpler change.  (Note, however, that I haven't reviewed his PR, so this isn't an endorsement.)

Also, I'm not actually sure if what the `Dop._repr_latex` was supposed to do, but I'm pretty sure it should have that last underscore.