Add Gradle files.

Not yet 100% finished, but already has the most things.
Add missing license headers in the source code.
IntelliJ doesn't do new lines at the end of Gradle files..
Merge branch 'master' of github.com:LapisDev/Commons

* 'master' of github.com:LapisDev/Commons:
  IntelliJ doesn't do new lines at the end of Gradle files..
  Add missing license headers in the source code.
  Add Gradle files.