OS X Compatibility fixes
Add Joe Smith to travis email notifications

This is primarily for the python side of the commons.

Testing Done:
https://travis-ci.org/twitter/commons/builds/36186847

Bugs closed: 326

Reviewed at https://rbcommons.com/s/twitter/r/1072/
Add to Application class a method to set the usage message automatically, to show the available commands.
Merge pull request #327 from simonrad/sradford/set_usage_based_on_commands

Add to Application class a method to set the usage message automatically.