ClassIcons: Addresses enable/disable bug, when player respecs.

For example, if we login as a shadow priest, produce few orbs, then respec to holy, then respec back to shadow, we won't have our shard bar back.
We'd better have PLAYER_TALENT_UPDATE event being always registered for priests and warlocks.
Added a call of Path function on disable inside of Visibility function, just in case some needs to perform something via PostUpdate function right after we hid classicons.
Few minor tweaks.