Add cards 'Ravenous Rats' and 'Mind Rot'

This commit also adds helper functions for asking the player to choose
from a set of cards.
Attackers without Vigilance are now tapped.
Merge pull request #52 from gseitz/tap_attackers

Attackers without Vigilance are now tapped.
Describing ChoiceCard now uses describeObjectByRef
Merge remote-tracking branch 'origin/master'
Add reveal functionality + Lilian's Shade
Merge pull request #51 from gseitz/reveal

Add reveal functionality + Lilian's Shade
New Card: Yeva's Forcemage
New Card: Titanic Growth
New Card: Vastwood Gorger
New Card: Spiked Baloth
New Card: Serpent's Gift
New Card: Sentinel Spider
New Card: Roaring Primadox
New Card: Revive
New Card: Quirion Dryad
New Card: Primal Huntbeast
New Card: Prey Upon
New Card: Plummet
New Card: Naturalize