Suit collars

Adds a collar overlay above the helmet layer if the suit has one
Suit needs an identically named sprite in icons/mob/collar.dmi
Suit also needs 'collar = 1' set in utility.dm

Trenchcoats are go!
Cleaned collar rendering code

Removed colon
Removed need for collar variable
Corrected TOTAL_LAYERS define
Tail rendering fix

Spotted this while working on collars code
Moved tail layer before hand layers, so tails don't render over held items
Merge pull request #4364 from Loganbacca/collars

Suit collars