Previously, we'd wait for a response before finishing app
initialization, meaning an overall slower startup. This fixes that.

Ref T572

Logs requests when --debug enabled, and always logs errors from the
check.

Ref T572

This keeps track when automated update check fails, and displays a
relevant message to the admin on /admin/updates

Ref T572

When a WriteFreely update is available, indicate this on the "Updates"
navigation item

Ref T572

Ref T572

- Tweak the copy
- Include link to download latest release
- Change the version status design a bit
- Restyle some text

- removes the parameter for newVersionCheck as was not being used
- changes newUpdatesCache to take expiry parameter for possible future
configuration option
- adds basic test quite to verify all cache fucntions work as expected

includes cache of latest version and page to view if updates are
available with a link to the latest update's release notes and a link to
check for the latest update now, refreshing the cache manually.