Add question: 'AskChoice'

AskChoice takes an optional question 'Text', and  a list of 'Choice'
values associated with a value of type 'a'. The client is responsible
for displaying the question and choices and inquiring an answer.
Add card 'War Priest of Thune'

This is the first card to make use of the new 'AskChoice' question.
Merge pull request #46 from gseitz/war_priest_of_thune

Add card 'War Priest of Thune'