Follow up of #1451

• Database properties dialog:
  • Do not show "Save sort order" - database sorts arbitrarily 😇
  • Do not show "Database protection" - makes no sense in a shared database setting
• Session restore: JabRef should open all [shared] tabs after startup
• Store last used connection in the "open remote database dialog"
• "open remote database dialog": "Connect" button should be disabled an label change to "Connecting...". Reason: Connection may take longer and pressing the button multiple times leads to error message dialogs. (You know, http://www.freemysqlhosting.net/ latency)