Pull avatar-related messages into their own plAvatarMessages project

[dpogue]

A lot of the avatar messages have dependencies on things from plAvatar (like plAvatarMgr) and that brings in a bunch of FeatureLib dependencies.

Once upon a time, it seemed possible to compile with a NO_AV_MSGS define to exclude the avatar-related messages for tools, but changing that between build targets would be super inconvenient.

My suggestion is to create a new PubUtilLib project and move the avatar messages there, and then update the things that actually use those messages to link against it. We might need to leave a few messages in plMessage if they are widely used, but stuff that involves plAvBrains and plAvTasks should be split out.

(Brought to you by my attempt to compile plFontConverter in mingw failing because of PhysX)