Fix compass and autoprefixer

Also renaming `.compass` to the more familiar name `config.rb`.
Fixing index.js requires

The AboutAction isn't working on liferay-app right now because of the require() calls on index.js. Prefixing with './' works as expected.
Refactors logic from `serve` task into AppRunner class
Adds unit test for AppRunner
Adds unit test for `clean` gulp task
Adds unit test for `build` gulp task