Added Vectors and Dyadics to IPython printing.

The Vector and Dyadic objects in the mechanics module have the capability to
print as LaTeX. I've added these to the init_printing `_can_print_latex` check
and now they render in the notebook properly. This fixes issue #2584.
Changed to \cdot for separating unit vectors and scalars.
Removed \cdot and went with no space.
Merge pull request #2687 from moorepants/mechanics-ipython

Mechanics Vectors and Dyadics print in LaTeX with init_printing()