Reconnect SessionController dropped from another window

It might not be the most elegant solution. @tcanabrava you know this code, any thoughts?

Test

1. Split views (Ctrl+()
2. Change terminal title ("Rename tab", Ctrl+Alt+S) for each split to "one" and "two"
3. Create new window (Ctrl+Shift+N)
4. Split views in new window (Ctrl+()
5. Change terminal title ("Rename tab", Ctrl+Alt+S) for one (any) split in new window to "three"
6. Show tab bar in first window (e.g. open new tab and switch back to first one)
7. Drag view named "three" from second window to first window
8. Switch focus between "one", "two" and "three". Observe tab title.

Results

Observed result (without patch)

Tab title follows title of focused terminal for "one" and "two". It does not change when focusing terminal dragged from another window ("three").

Expected result (with patch)

Tab title follows title of focused terminal for all three terminals.