This commit changes the API for registering the plugin config
page nav configuration from a server-side to a JS one;
there is no need for it to be server-side.
It also makes some changes to allow for 2 different ways of displaying
navigation for plugin pages, depending on complexity:
* TOP - This is the best mode for simple plugins without a lot of different
custom configuration pages, and it reuses the grey horizontal nav bar
already used for admins.
* SIDEBAR - This is better for more complex plugins; likely this won't
be used in the near future, but it's readily available if needed
There is a new AdminPluginConfigNavManager service too to manage which
plugin the admin is actively viewing, otherwise we would have trouble
hiding the main plugin nav for admins when viewing a single plugin.
This commit adds new plugin show routes (`/admin/plugins/:plugin_id`) as we move
towards every plugin having a consistent UI/landing page.
As part of this, we are introducing a consistent way for plugins
to show an inner sidebar in their config page, via a new plugin
API `register_admin_config_nav_routes`
This accepts an array of links with a label/text, and an
ember route. Once this commit is merged we can start the process
of conforming other plugins to follow this pattern, as well
as supporting a single-page version of this for simpler plugins
that don't require an inner sidebar.
Part of /t/122841 internally
This tab doesn't really provide anything useful, and can be quite
confusing in some cases. Each plugin is already listed below, and
you can navigate to their settings from there. We want to move away
from the catch-all Plugins category for site settings. Core plugins are
not shown in this list as at 97a812f022.
Previously if a specific plugin route was not available (e.g. there was an error loading the plugin's JS due to an ad blocker), the entire page would fail to load. This commit updates the behavior to catch this kind of issue and display a user-friendly message at the top of the screen.
