Fix disabled groups after screen rotation

isDissolved was reverted back to LiveData that only shows a dialog when the activity was first opened.

Test instructions:

• create or join private group, enter the group, rotate screen and ensure group doesn't get disabled/greyed out
• join private group shared by contact, let contact dissolve the group and ensure
  • you get a dialog and the group gets disabled after the contact has dissolved the group
  • the same happens if you re-enter the group again
  • rotating the screen in the disabled group doesn't re-show the dialog
  • the group is greyed out in the group list and removable there