[EMF] Entity Model Features

RC-3

• re-enabled an option for testing in RC-3 that allows using minecraft's internal MathHelper class for some math methods as opposed to regular Java's Math methods (doesn't really seem to be a performance benefit in ym testing, just trialling this before I decide whether to delete this old code)
• fixed top level jem texture overrides
• fixed book.jem's flipping page pivots
• changed some default config settings for performance boosts
• fixed a forge crash
• fixed armor stand armor models not remapping the headwear part
• fixed guardian and elder_guardian OptiFine part name mappings ("eye" did not work)