Persistence for the remote database location + some warnings fixed

 1. Fixed some javac warnings :
   * .show()-> .setVisible(true
   * .getText()->getPassword()
2. Implemented persistency for remote reporsitory URLs.
   It works similarly to the android version and persists the
   HTTP url, user name and password.
   On startup it checks if there's an URL persisted and if there is
   it overwrites the db file location with the download.