Make Tizen task manager recognize xwalk.

Tizen task manager expects that any application is in /opt/usr/apps/, so this
patch makes xwalk live in /opt/usr/apps/

The task manager gets a package name from an executable name and our executable
name is xwalk, so this patch changes xwalk package name from crosswalk to xwalk.

The task manager expects that a package id is different from a package name, and
common package id is org.tizen.XXX, so this patch changes xwalk package id from
crosswalk to org.tizen.xwalk.

NOTE: we can use either /opt/apps/ or /opt/usr/apps/, and I choose
/opt/usr/apps/, because
- /opt/apps/ is symbolic link to /opt/usr/apps/.
- xwalk forks sub processes that are launched using original path.
So, if choosing /opt/apps/, the task manager can not recognize xwalk.

BUG=https://github.com/otcshare/crosswalk/issues/411

NOTE: It is necessary condition, not sufficient condition. Tizen task manager can not recognize xwalk yet.
If you change xwalk_main.cc as follows:
int main (...) {
  while (true) sleep(100);
  return 0;
}
the task manager can recognize xwalk after this patch.
I assume that forking sub-process prevents the task manager from recognizing a process. I'm working progress about it.