Submodule track specified commit id
When we run git submodule update --init
The master branch in submodule will always be the latest version.
We want to track specified commit of submodule, because the submodule
will be updated, and will not work on our crosswalk sometimes, such as
MemoryGame from 01.org
Solution:
1: Remove '-u' flag, to avoid user update web apps themself.
2: Create a new branch named 'for_crosswalk', which will track specified commit id
3: Revert MemoryGame to commit:Moved app into app/.

BUG=https://crosswalk-project.org/jira/browse/XWALK-103
Merge pull request #26 from kurli/submodule_track_commit_id

Submodule track specified commit id