Clean up existing mypy issues, run in CI.

[DanAlbert]

This is the first step for #160.

Each commit here was already squashed, so should be independently reviewable (and can rebase the PR when submitting and it won't make a mess of the branch history).

There are four commits here:

1. Fixes/deletes some files that were just plain broken in the current repo. Not all the vehicle/ship/etc class names were fixed after one of the recent DCS exports. I deleted one since it's presumably unused, but I fixed templates.py since it was used elsewhere. I can resurrect the deleted file if preferred, but it seems no one uses it because it's been broken for a while.
2. Latest export before mypy changes. I needed to tweak a few things in the exporter to add missing annotations and fix a bug or two, and this commit makes it easier to see the result of those later changes.
3. The interesting part: cleans up all the mypy errors that exist for the default(ish) configuration. I did punt on the terrain files since that exporter also needs to be fixed, and it's a lot more annoying to run those so I haven't gotten to them yet. For now they're disabled in the mypy.ini, but no other mypy configuration is used beyond the default yet.
4. Run mypy as part of the GitHub action to prevent regressions.

Most of the fixes needed were pretty straightforward. New base classes, correcting existing annotations, adding missing annotations, introducing a few generics, etc. A very small number of APIs changed, and mostly only to correct the signature to the actual behavior (a handful of functions treat all arguments as optional even though if that behavior is relied upon the function will raise). Shouldn't be any serious impact from the changes.

Many of the function-internal issues were fixed by adding an assertion or a type-check that raises since the existing APIs can't be made type-safe without being more invasive, and IMO that's better left until after mypy is fully deployed. It might also break existing users.

[DanAlbert]

For whatever reason my first attempt at disabling the checking for the terrain files worked on my machine but not in CI. Fixed now and ready to merge as far as I'm concerned. I'll be following up with the other items mentioned in the bug.