[Application] Move logic for launching app to ApplicationSystem

Main motivation was to abstract this complexity away from
XWalkBrowserMainParts. ApplicationSystem now deals with the different
ways to pass the app id in the command line.

It turns out that after the refactoring, we can see that Tizen sensor
initialization wasn't being called in some cases when running
applications.
[Application] Remove unused includes from XWalkBrowserMainParts