[#1336] First pass at attack modifier regions & auto-populating other attack modifiers based on targeting

When attacking (rolling a trait from a weapon-type item):

• If standing in a region with the new behavior in it and "Unstable Platform" checked, and the weapon is ranged, pre-populates the "Unstable Platform" modifier in the roll dialog
• If targeting tokens, the "worst" possible negative modifier for the targeted tokens' covers/illuminations (as defined by the regions they are standing in) will be pre-populated in the roll dialog

Also... a lot more. See changelog for full details.