Change PlanningPokerGame model to store requirement IDs instead of Requirement objects

Authors: bbiletch, rbkillea, mamora
Merge pull request #96 from bbiletch/sbl-dev

Change PlanningPokerGame model to store requirement IDs instead of Requirement objects
Checked out by Ben Korza
benkorza
Merge pull request #98 from bnurbekov/sbl-dev

Header: Adds the new image for the card deck
Header: Makes the "Modify game button" disabled by default

Reported-by: bnurbekov, mamora
Signed-off-by: Batyrlan Nurbekov <bnurbekov@wpi.edu>, Miguel Mora
<mamora@wpi.edu>