Added Travis CI build/test config using xctool. 

I had to disable the unused variable warnings on the AFNetworking Mac dependency to get this to build because we're stripping assertions from the Release build of AFNetworking. Removing the assertion means that the variable is unused and as warnings are treated as errors, the build breaks.

I think this is better than not stripping the assertions as it's an external dependency but let me know what you think. The warning is still logged by xctool, just not treated as an error.

Everything is building and tests are passing :thumbsup: