Almost fix filtering in the guide

Almost fix filtering in the guide

Still has an issue: doesn't work properly for Gametypes and Mutators.
- Method used was filtering based on .m_name, however Gametypes and Mutators don't use .m_name (yet), they use .message.
- This can easily be fixed by just changing the macro to use .message for those two, but a better approach should be used, so I'm intentionally pushing slightly-buggy code in hopes a better approach will be found.
Needed a bit of reworking of some functions in menu/guide/entries.qc so that MENUQC would stop crashing, added comments to help clarify code.