Rollback options should be greyed out if not available

Currently the right click menu shows all rollback options (start of current turn, start of previous turn, etc.) as choosable even if it cannot be rolled back that far.

disable the options which are not available, rather than showing a popup when an unavailable one is clicked would be a small but nice improvement.

Start by locating the right-click menu that contains the rollback options and the existing handling for unavailable rollback choices. Check how the menu determines which turns can be rolled back, then make unavailable options visibly disabled instead of opening the current popup. Done means each rollback option reflects whether that rollback is possible.

Written by the indexing model from the issue text.