Add a version tag to PartMessageServiceInitializer

Actually, the KSPAddon is now a wrapper around the original
PartMessageServiceInitializer class, which is no longer an addon, it just
provides some static functions for the addon to call. This seems to fix the
problem with multiple versions of KAE not working properly, the cause of
which seems to be either KSP or Unity (unknown which) calling the same
class/assembly for every assembly. Giving the class a reasonably unique
name seems to fix the issue.

It is not yet known whether the compatibility checker or the tweakables
code needs similar, so only PartMessage is done at this stage.
Add a little debug output.
Add a message to not edit the generated file.