fail of the return code from the callback wasn't true in one place, but not in two others -- also set it to work if the return code is undefined, this means to force it to fail, one must specifically return a 0 or false
fix issue brought up by bull5_i in disqus comments)
Added optional afterAdd and afterDelete callbacks
Let onAdd/onDelete callbacks modify control flow
If false is returned from the onDelete callback, the delete will not be performed. This usecase can be used for tag clicks that should not delete tags.
properly to the callback functions