This renames the modules.

The groupId is now `com.f2prateek.progressbutton`; not `com.fprateek`
The `library` module is now named `progressbutton`
The `samples` module is now named `progressbutton-samples`

The artifactId's are unchanged.
Merge pull request #19 from f2prateek/rename-modules

The groupId is now com.f2prateek.progressbutton; not com.fprateek
The library module is now named progressbutton
The samples module is now named progressbutton-samples