We currently have three methods of choosing locations for TGOs:
1. From the campaign miz
2. From the per-CP mizdata files
3. Randomly
Move the selection among these sources into a single place and use it
everywhere that we search for a TGO location.
Longer term methods 2 and 3 will be removed.
Defining a campaign using a miz file instead of as JSON has a number of
advantages:
* Much easier for players to mod their campaigns.
* Easier to see the big picture of how objective locations will be laid
out, since every control point can be seen at once.
* No need to associate objective locations to control points explicitly;
the campaign generator can claim objectives for control points based
on distance.
* Easier to create an IADS that performs well.
* Non-random campaigns are easier to make.
The downside is duplication across campaigns, and a less structured data
format for complex objects. The former is annoying if we have to fix a
bug that appears in a dozen campaigns. It's less an annoyance for
needing to start from scratch since the easiest way to create a campaign
will be to copy the "full" campaign for the given theater and prune it.
So far I've implemented control points, base defenses, and front lines.
Still need to add support for non-base defense TGOs.
This currently doesn't do anything for the `radials` property of the
`ControlPoint` because I'm not sure what those are.
Like with deleting waypoints, these will degrade the flight plan to the
2.1 behavior.
Ascend/descend points aren't in use any more, so I removed those.
