Instagib and LMS: fix a few issues with instagib items and in particular extralife
- Instagib: fix items from other games not getting replaced by instagib powerups
- Instagib: fix ammo from other games not getting replaced by vaporizer cells (if enabled by the g_instagib_ammo_convert_ cvars, disabled by default)
- LMS: fix megahealths from other games not getting replaced by extralife
- LMS: if normal items are enabled don't convert megahealth to extralife
- LMS and Instagib: fix extralife not counted in the Itemstats panel and wrongly displayed in the Pickup panel