Allow caching links from a menu

Problem/Motivation

While it is helpful to be able to manually enter pages to add to the CDN cache, it would be useful to be able to automate this via the menu system.

Proposed resolution

An option would exist on the settings page to select menus. The selected menus would have its items all checked on the CDN cache.

Remaining tasks

Build the functionality.

User interface changes

An option would be available on the CDN settings, or maybe an extra tab, to select menus which would be used to identify links to cache.

API changes

TBD

Data model changes

n/a