The previous flight plan only makes sense if the convoy will make it a
significant distance from its starting point. At road speeds over the
typical mission duration this is not true, so we can actually plan this
as if it was a strike mission near the origin point and that's close
enough.
There's some cleanup work to do here that I've added todos for.
Fixes https://github.com/Khopa/dcs_liberation/issues/996
A CP with a factory would be able to supply itself, but was not in a
supply route if it was the only connected friendly CP. When the player
starts with only one base against an enemy base this meant that it was
in no supply route, causing it to not be a recruitment location or a
place to buy more than a reserve of vehicles automatically.
This adds the models and UIs for creating ground unit transfer orders.
Most of the feature is still missing:
* The AI doesn't do them.
* Transfers can move across the whole map in one turn.
* Transfers between disconnected bases are allowed.
* Transfers are not modeled in the simulation, so they can't be
interdicted.
https://github.com/Khopa/dcs_liberation/issues/824
