Add option to save open connections on exit and restore them when starting

[jochenwierum]

The idea is to add a checkbox in the options which lets the app save a list of open connections when it gets closed. When restarting (and the flag is present in the config) the list could be read and the connections will be opened again.

[hapm]

This is strongly realted to #12 and #34 . Would be nice if the profiles in the list have 2 different states.

• "restore connection state": will restore the latest known state for the profile (connect, if it was connected on shutdown)
• "auto connect": will always try to connect the profile on startup, regardless of its last state.