Improve Publish Page workflow

Hitting Publish Page should perform the action, display a flash message to let the users know the result, and keep the current page open (do not redirect to index).

That should be the workflow either on code editor or visual editor pages.

Related to https://github.com/BeaconCMS/beacon_live_admin/issues/175

Start at the Publish Page action in the code editor and visual editor pages. Verify the workflow for both editors: publishing should show a flash message describing the result and keep the current page open instead of redirecting to the index; issue #175 provides related context.

Written by the indexing model from the issue text.