Extend editing environment for Info pages and Events

[darabman]

In order to improve the speed of adding content, setting up a lanager session for a new party, and to eliminate the risky practice of granting other admins access to the raw tables in MySQL, I think the following functionality should be added:

• An info admin page and an event admin page with the functionality for Creating, editing and deleting entries from within lanager. Such a page need be nothing more than a list of event/info records (likely ordered by the Title field) with "Edit | Delete | Visible" buttons by each entry, and a 'New' button above the list.
• Editing the entry would take the user to a form populated with the data for that entry, not dissimilar to the exisitng event creation form. Clicking 'New' from the list of entries would understandably take the user to a blank form, with a submit button.
• Only admin users should have access to these pages
• A collapsible frame alongside the Edit/New form would show a Markdown 'cheat-sheet' as a reminder for editors.
• The 'visibility' of events and info pages should be set-able, meaning that commonly-used items could be disabled, edited and re-used without removing them from the databse outright

[ilumos]

Completed in zeropingheroes/lanager-core@b71d10e