desktop-pwas: Move 'Add to Shelf/Desktop/Applications' to the top level

This is done only if the ExperimentalAppBanners feature is enabled.

Also re-arranges the strings and guards in them the grd file instead of
in c++.

Bug: 629725
Change-Id: Iec496f5ee9c4729fdecc272223e66c5abd93a494
Reviewed-on: https://chromium-review.googlesource.com/658580
Commit-Queue: Giovanni Ortuño Urquidi <ortuno@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501197}
3 files changed