#372b Some file rearrangement in the test suite

When I started work on #426, I realized that test_SBProfile.py was getting pretty long and unwieldy.  So before starting on that I decided to split it up into more manageable pieces.

This is really a continuation of issue #372 that involved splitting up base.py.  I followed basically the same structure as what I did there with base.py.  Now there is:
- test_base.py, which just tests the basic objects (gaussian, exponential, sersic, etc.)
- test_compount.py, which tests add, convolve, autoconvolve, etc.
- test_transforms.py, which tests shear, shift, magnify, etc.

And some of the items were moved into other existing test files that seemed more appropriate.  e.g. the test_sbinterpolatedimage unit test was moved into the existing test_interpolateimage.py file, which has other unit tests relevant for InterpolatedImages.

I also normalized the case convention on the file names.  Most of our test files are all lowercase, so I made the few that weren't to also be lowercase.

There aren't really any code changes here, just file restructuring.  So after a couple people test that I didn't break anything, it can probably be merged in pretty quickly.  Then I'll handle merging it into existing branches to handle any possible conflicts that I introduced with things people are currently working on.