Display a warning if saving a backup plan that does not have a destination.

External drive plans could be invalid if user never plugs in a destination drive. If he does, select it automatically and potentially save a mouse click. And minimize risk of forgetting to select it after plugging in.
(cherry picked from commit 6d8bb64ee2dff68b826aeab2ebc7d20095c89633)

Conflicts:
	kcm/driveselection.cpp
Add italian, german and tagalog translations.

Also update swedish with newly added string.