Some small cleanups.

 - Simplify .gitignore
 - Fix warning + errors during build.
 - Rename and move string util method.
 - Introduce GeoServer data object to store API access parameters.
Use GeoServer instance for server parameters in REST reader.
Use slf4j with logback for logging.
Replace url, username and password with GeoServer instance.

 - Yes, I'm stuck on a train.