update gradle build file.

Change-Id: I19b14933e677117ac075c385d01261e818c500e6
fix pre-commit scripts.
fix CDOJ-UI gitmodule URL.
Merge pull request #2 from pfctgeorge/fix-submodule

fix CDOJ-UI gitmodule URL.
update ui submodule.
Merge pull request #24 from pfctgeorge/fix-submodule

update ui submodule.
fix choose language in problem show.
Merge pull request #25 from pfctgeorge/hotfix-choose-language

fix choose language in problem show.
Merge pull request #27 from UESTC-ACM/master

release: v20140219-1200
release issue: #26