Rename all X_headwear color as X_hat color

BUR #559 is pending approval.

create alias black_headwear -> black_hat
create alias white_headwear -> white_hat
create alias grey_headwear -> grey_hat
create alias red_headwear -> red_hat
create alias yellow_headwear -> yellow_hat
create alias green_headwear -> green_hat
create alias blue_headwear -> blue_hat
create alias purple_headwear -> purple_hat
create alias pink_headwear -> pink_hat
create alias brown_headwear -> brown_hat
create alias orange_headwear -> orange_hat

consistent with danbooru.
if after this, there are several post with headwear that do not qualify as "hats", I will update it manually if needed

Danbooru doesn't have the colored headwear tags aliased to anything. They are deprecated instead, which makes sense because if the above BUR goes through, a black helmet would be tagged as black hat as well.