Fixes implementation of tintColorDidChange. 

I was experiencing a crash in an app that was based around an older version of TTTAttributedLabel. It was crashing trying to add/remove the active/inactive attributes. 

It seems right to use active/inactive link attributes instead of the vanilla link attributes here, allowing you to properly opt out of this behaviour. 

A better way to detect `isInactive` was mentioned in  #352, since there was no PR for that, I have included that here too.