Change application information.

* Move SDK versions to Gradle.
* Move application name to resources.
Add license headers to resources.
Change resource names.
Change navigation drawer style a bit.
Change servers spinner to show only active ones.
Add Timber dependency for logging purposes.
Introduce API adapter class for more centralized API configuration.

It would be great to keep a single RestAdapter, but API urls are always
different, so we need to be more flexible.