Refactor logging

[rfc2822]

• Decouple logging from Logger object, which has an Android dependency. We use the standard Java java.util.logging.Logger in DAVx5, so there's no need for an Android dependency to get the logger.
• Separate concerns: LogManager is now managing which handlers are active; the handlers do whatever belong to their responsibility (for instance the "Verbose logging" notification is now shown by the LogFileHandler)
• Provide injection of Logger (gets Logger.getGlobal())
• New preferred way of getting the logger is either
  • over injection: @Inject logger: Logger,
  • or without Android/app dependency: [j.u.l.]Logger.getGlobal()
  • or if the logger needs to be customized (for instance like in DavResourceFinder): [j.u.l.]Logger.getLogger(javaClass.name)