jak3: speedrunner mode

[Hat-Kid]

Base implementation of the popup menu and speedrunner mode in Jak 3. Autosplitter is untested because I'm on Linux.

Also a couple of other misc changes:

• Model replacements can now have custom bone weights. Needs the "Use Custom Bone Weights" property (provided by the OpenGOAL Blender plugin) enabled in Blender.
• Better error message for lump syntax errors in custom level JSON files.