Reactions

* Added spell actions for when the spell gets the killing blow. If a reaction is used for that, then it won't also use any normal hit reactions if they exist.
* Added a help icon thing beside the spell/event action dropdown list to show a tooltip of notes for it (like what main variables are used).
* Fixed a bug with checking if spells are successful that could have potentially used reactions twice, but don't know of any cases of that besides with the spell killing blow thing just added.