Secure/Defend new expansions

[ImpulseCloud]

Send an army group to secure/defend a new expansion (marked CONTESTED) to ensure any enemy is removed and worker will be safe while constructing new TownHall.

[ImpulseCloud]

A new Expansion variable 'signal' can be used with values (NONE, ATTACK, or DEFEND) to direct the army where to go.

Army will stay at Expansion with DEFEND signal, until the 'main attack' trigger is hit, whereby it will then proceed to the nearest ATTACK signal expansion, and 'clear' that area of enemies, then proceed to the next nearest ATTACK signal expansion, until it reaches Enemy starting location.

RE: "supporting marking enemy expansions without particular tag"
If there are non-Townhall enemy buildings in a region/expansion, it should be set as CONTESTED and set 'signal' to ATTACK.