Add Uninstall UI for Crostini Apps

Add UI to handle the "uninstall" menu option when right-clicking on a
Crostini app. This change brings up a confirmation dialog; if the user
confirms, it starts up the container and sends an uninstall message.

UI mocks https://docs.google.com/presentation/d/1akjEdjidRcMH54SK9zMmQVIPaPkwVuatXuKZLJKUqzA/edit

Several known bugs:
 * chromium:909071
 * chromium:909063
 * chromium:898295
so this is behind a flag (CrostiniAppUninstallGui)

BUG=chromium:822514
TEST=Uninstalled multiple applications. Uninstalled applications at the same time for
queuing. Closed notifications while applications were uninstalling or queued. Installed
and uninstalled applications at the same time.

Change-Id: If5bb80cb867e55c3f082c40f89357f05db151985
Reviewed-on: https://chromium-review.googlesource.com/c/1275292
Commit-Queue: Ian Barkley-Yeung <iby@chromium.org>
Reviewed-by: Timothy Loh <timloh@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Anand Mistry <amistry@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616567}
27 files changed