[Runtime] Move install/uninstall/update actions into FILE thread in service mode.

In Crosswalk service mode, some actions like install/uninstall/update
will take place in UI thread, and these would block running web
applications if it takes a long time. So move these slow methods into
FILE thread.
application service was not designed to be used from multiple threads, it "lives" in UI thread. Looks like it's not quite safe to invoke it from file thread.