GitLab

This CL moves the non-extensions-specific concepts of External Web Apps,
System Web Apps and Policy Web Apps into the generic web_applications/
level, rather than being in web_applications/bookmark_apps/ which was
extensions specific.

The tests remain in bookmark_apps/ because they have some dependencies
on extensions e.g installing and explicitly checking the existence of
an app through the extensions system. Tests without extensions dependencies
will be moved in a follow-up patch.

Bug: None
Change-Id: I9d9bca55e73a46ef5ad2781f6eca29416059d6b6
Reviewed-on: https://chromium-review.googlesource.com/c/1333012Reviewed-by: Ben Wells <benwells@chromium.org>
Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Commit-Queue: calamity <calamity@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608687}