Header: Implemented card deck for requirement estimations

Adds a card deck for requirement estimations to the upper left corner of
OverviewPanel tab.

Reported-by: bnurbekov, zpak, hlong290494
Signed-off-by: Batyrlan Nurbekov <bnurbekov@wpi.edu>
Merge pull request #59 from bnurbekov/sbl-dev

Header: Implemented card deck for requirement estimations
Tested by: Alec Thompson