Added integration with Travis CI

As [Travis CI](https://travis-ci.org) now supports objective-c and [xctool](https://github.com/facebook/xctool), which allows to build and run tests from CLI with ease, is released. It's super easy to have continuous integration for open source projects! :)

I'm happy to suggest to add support for Travis CI for MTDates! :) With these changes each time when somebody pushes something all tests will be run on Travis CI. In case of failure contributor and repo owner will get notifications.

@atomkirk the only thing you need to do after merging this (I hope you will accept this) is to login into [Travis CI](https://travis-ci.org) with your Github account. On [your profile page](https://travis-ci.org/profile) enable sync for `mysterioustrousers/MTDates` repository. It will add a hook to run tests each time when somebody pushed into repository.

Also you can find an example of tests run for MTDates on Travis CI [here](https://travis-ci.org/yas375/MTDates).