Traffic++ intersection editor

Restored saving of timed node groups which was accidentally removed in previous update.

Fix for null reference exception when saving a new city.

. GUI for Improved AI tweakable parameters
. toggle for Traffic Manager / Improved AI lane interaction
. no despawn
. saved data integrity checking on load

Fix for bug that prevented u-turns in the pathfinding code. Also made the two variables mentioned in the description static so only one thread needs to be updated in ModTools.