Update project layout to recommended standard

This largely moves files and folders around to places Google nowadays
recommends.

This also adds the gradle build tool. The benefit is dependecy management
(libraries can be pulled in automatically) and a consistent build system
throughout the development machine and continuous integration.
Add Travis CI support
Update descriptions

Update path mentioned in descriptions to a more general setup.
Merge pull request #2 from mtneug/modern-structure

Modern structure by Matthias
Travis CI, Gradle, Descriptions updates