Implement type-dependent classes for rebel AIs

[jaj22]

What type of PR is this.

1. Bug
2. Change
3. Enhancement

What have you changed and why?

Implemented type-dependent classes for rebel AIs. This makes the unit type icons in the command bar work correctly (medics and engineers now have the appropriate symbol), plus the overlay names no longer all say "riflemen". Petros is now "officer", for example.

Each element of customUnitTypes now has an additional parameter for the unit class to be used for that unit type. These are varied for rebel units only, as we don't much care about the UI for enemy troops.

Also fixed some misnamed loadout -> definition variables, and fixed the incorrect loadout count debug text. Definitions already had an extra parameter of unit traits, so the format apparently changed at some point.

Based on vn-development so that we can get the merge conflicts in early.

I haven't checked the code for civ creation but they seem to work for whatever reason. Enemies should be fine.

Please specify which Issue this PR Resolves.

mentioned in #1914

Please verify the following and ensure all checks are completed.

1. Have you loaded the mission in LAN host?
2. Have you loaded the mission on a dedicated server?

Is further testing or are further changes required?

1. No
2. Yes (Please provide further detail below.)

How can the changes be tested?

Enable command bar and the server difficulty option that gives you information about your troops on mouseover. Recruit all the different rebels and look at them. Also check out Petros. He likes it.

[Bob-Murphy]

Tested and working.
To me the code looks good but I rather wait for a second pair of eyes on that.