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