Tweaked and reworked the BT editor to allow for multiple modes (like the Blueprint Editor).
If a behavior tree uses a Blackboard, that blackboard is editable in the same asset editor, under "Blackboard mode".
Fixed a number of issues with re-focussing the BT debugger (and some issues that arose when switching BT editor modes). Debugging info should now be properly displayed when selecting AIs, switching modes, starting up the BT editor while playing etc.
Fixed a breakpoint bug where debug pause would be toggled rather than enabled, causing the game to run for a short time.
Added new icons for BT & BB modes.
Added various new guards against nullptr dereferences.
Displayed Actor label rather than FName when choosing actors to debug.
TTP# 337108 - Behaviour Tree Editor: Integrate Blackboard Editor into Behaviour Tree Editor
reviewed by Chris.Wood, Lukasz.Furman
[CL 2102883 by Thomas Sarkanen in Main branch]
