Improve shared database feature

[koppor]

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)

[Siedlerchr]

• Use AssumeTrue(DevEnvironment.isCIServer()) switch to disable database tests locally. Prevents failing tests, if no db is running locally.

[koppor]

Alternative solution: #1705 to make it explicit when to call the database tests. I know that one can also run the tests using the ide, but I would like to keep the consistency with our integration tests. Please follow up at #1705.