[TIMOB-20148] Improvements on tio2 unit testing

The possibilities of our new ti2 unit tests are GREAT. Here are some thoughts on how we could improve the structure of our unit tests to keep it clean over the next years: - Folder structure like done in the docs: /Ti/UI/Label.js instead of ti.ui.label.test.js - Require tests automatically instead of linking every test manually in the app.js - Place asset files (images, videos, text files, etc.) in an appropiate folder structure e.g. /assets/images/ and /assets/audio/ etc. The current structure can be found [here](https://github.com/appcelerator/titanium_mobile/tree/master/ti_mocha_tests).