Write a test suite

[jkudish]

I've started writing a test suite for the plugin that incorporates phpunit testing for plugin internals and casperjs testing for admin interactions, saving, etc.

Development will occur in the tests branch for now with the intention that the tests will be merged into master afterwards. Version 0.8 will include these tests. The tests will run using travis-ci and the handy github integration.

I'd like to have tests written for all of the major features of the plugin, including:

• [x] adding groups
• [ ] adding fields
• [ ] adding multifields
• [ ] displaying groups as expected
• [ ] displaying different field types as expected
• [ ] displaying multifields as expected
• [ ] saving different field types
• [ ] saving multifields