Allow `civicrm_menu` to store new data in generic column

Background
==========

To fix CRM-20924 and CRM-20926, we need a place to store per-page
information about the IDS configuration.

More generally, as we continue adding features through extensions, we should
anticipate that the route metadata will expand in ways that we can't
anticipate.  Adding a general-purpose serialized field will help us define
new behaviors through extensions.

Before
======

All metadata in the routing table (`civicrm_menu`) had to stored in a
separate SQL column.

After
=====

Any unrecognized fields will be stored and loaded from the column
`module_data`.

Acceptance Criteria
===================
 * New data can be stored in `civicrm_menu`.
 * Unit-test verifies above.
 * Navigation menu continues to work in UI.
 * The "Administer" screen (which has special menu-handling) continues to work in UI.