This commit introduces a little bit of duplication
since the old plugin UIs not using the new plugin show
page look different from ones like AI and Gamification
which have been converted. We can use the new admin
header component on the plugins list, but for the other
pages we are manually rendering a breadcrumb trail and
the list of plugin tabs.
Over time as we convert more plugins to use the new UI
guidelines and show page we can get rid of this duplication.
* Simplify config nav link generation to always inject the Settings
tab
* Auto-redirect to the first non-settings config link (if there is one)
when the user lands on /admin/plugins/:plugin_id
* Add `extras` to admin plugin serializer so plugins can add more
data on first load
* Add PikadayCalendar page object for system specs, extracted from the
CalendarDateTimePicker to make it more generic.
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.
