made test_format.py un-executable, so that nosetests runs it. Fixed pep8 issues that this uncovered.
pep8
added try-except block around importing matplotlib
fixed warnings issued by 'python doc/scripts/docgen.py --test'
Added skip_if_no_sklearn() calls to avoid UserWarnings about missing sklearn in Travis
removed the skip_if_no_XXXX() calls added in the previous commit, aded matplotlib installation to .travis.yml
removed matplotlib installation from .travis.yml, put matplotlib imports within try-except blocks in browse_norb.py, browse_small_norb.py, commented out test that was causing mystery crashes in Travis, for later investigation
Merge pull request #1159 from SuperElectric/pep8_nosetest

made test_format.py un-executable, so that nosetests runs it.