Core/Scripts: Add new SpellScript hook

Adds SpellScript hook to execute scripts after succesful dispels, example could be warlock pets Devour Magic, which should only trigger when succesfully dispelling an aura.

Please discuss/feedback whether its done correctly and/or if its missing something, as in other or more parameters than effect index etc. i know its not like the other effecthandles, but it does bind to a single effect and should/could be treated the same way.
`for (SpellScript::CastHandler const& hook : ss->BeforeCast)`
use const ref in such places to avoid unneeded copies