Instead of polling for all the requirements every time isEnded() is called cuts back to only polling for new users when it's most necessary: if a game would otherwise end due to all users voting.
Merge team9dev into stabilizeUserPolling
Fixes endDate not being set when game is ended.

Author: nfbrown
Merge pull request #158 from dbeckwith/stabilizeUserPolling

Stabilize user polling
Save + update button remains active even if value has been saved in planningpoker already, as long as the value is valid and it is not the value in requirement manager.
Fixes NullPointerException caused by sorting the tree when closing a game that is in progress.

Author: nfbrown
Merge pull request #159 from dbeckwith/enableUpdateReq

Save + update button remains active even if value has been saved in plan...
Merge remote-tracking branch 'origin/team9dev' into HALP
refactor tutorial switch statement into functions, with javadocs