Trunk 3415 Add ability to update css through webapp

3 commits comes from https://github.com/ehsdev/openmrs-module-custombranding repo, without them original custombranding repo didn't build
If it is really an error then you should rethrow the exception instead of returning null and do not log it at this point. Also prefer log.error("...", e), log.debug("..", e), etc. so that the whole stack trace is logged.