Order queuing for formations

[Philip]

When a group of units is ordered to do anything other than walk, the formation controller disbands and each unit performs the order individually. If the formation controller had queued orders, they get lost.

Instead, units ought to stay associated with the formation controller while they're individually carrying out the action (attacking, gathering, etc). The formation controller should detect when its order has been completed (target died, resource exhausted, etc) and then regroup the units and move onto its next order.

[leper]

In 11876:

Add repair order queueing to formations. Refs #592.

[leper]

In 12911:

Formation order queueing. Fixes #592, #593 and #1716.
Allow changing the formation, while under attack. Fixes #1624. Patch by Simikolon.