Update to py37

[RobertArbon]

• [x] Implement feature / fix bug
• [x] Add tests
• [x] Update changelog

Currently Osprey doesn't build with Python 3.7 or higher. This is due to a number of problems which this PR fixes.

1. No more sklearn.externals.joblib. system joblib is imported now. Datasetsloader default is system joblib.
2. MSMBuilder not compatible with py37. MSMBuilder tests are now optional. Changed build recipe to exclude MSMBuilder.
3. Pandas ix is now fully deprecated. Using .loc instead.
4. numpy skipif decorator not found. changed import statement to find it.

Also changed some other things:

4. Made tests of optional packages (GPy, MSMBuilder, Hyperopt) dependent on the try/except pattern rather than the module in sys.modules pattern.
5. Included basic PyEMMA test.
6. a test that was using MSMBuilder now uses sklearn instead.
7. yaml.load requires Loader variable. Not essential but fixed anyway.
8. check_scoring import deprecated in next sklearn version. changed import statement to be future comptible. Not essential.