refactored org.geogit as org.locationtech.geogig
Rename all classes with geogit on its name to contain geogig instead.
change all references in code to geogit to geogig
change all geogit references in non-code files under src/ to geogig.
updated docs to mention geogig instead of geogit. Except some http URLs.
remove GPL mention for the geoserver plugin as its not part of this codebase anymore