[App Management] GetApps returns array of initial apps.

This CL changes the GetApps function of the app management PageHandler
to return the initial apps directly rather than calling onAppsAdded,
which simplifies initialisation of the ApiListener. It also changes
the onAppsAdded function to onAppAdded.

Bug: 906508
Change-Id: I649530920dfcce9d3998d9b2eda0320244ced15c
Reviewed-on: https://chromium-review.googlesource.com/c/1393587
Commit-Queue: Reka Norman <rekanorman@google.com>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: calamity <calamity@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619894}
10 files changed