Improve multiroot support

[mlewand]

• Add handling for detached (removed) roots.
  • Currently there's no difference.
• Set data dialog should allow to chose which root will receive data change.

[mlewand]

As of implementation, we removed detached root in the initial solution.

However @scofalik pointed out that it could be useful in some cases to actually be able to see detached roots (to make sure that what you did works as expected and that the data there is emptied correctly).

Wondering what is the best solution for that. Following comes to my mind:

• Just append a " (detached)" text to it's name and sort them to be at the end of results (but before graveyard).
• Add opt-in flag setting to toggle visibility of detached roots.

I like the first solution more as it's much cheaper to implement and has 0 learning curve.

[scofalik]

+1 for "just append".