Possible 'Pet Missing' Hint Feature

Issues: 
* Only works in combat, like all hints. 
* Not sure why UNIT_PET works in the rule. I left it in anyway.
* Requires adding ```HasPetSpells()``` to SafeEnv.

```numSpells, petToken = HasPetSpells()```
```numSpells (Number) The number of pet spells/skills. nil if you do not have a pet out.```
```petToken (String) Pet type, can be "DEMON" or "PET".```

Tested in game it works fine for DK and Hunter. Obviously will work for Warlock too.