Allows us to check for the licence finder beyond the QueryBuilder class.
The ContentItem model also seems a more appropriate place to verfiy the
exact finder content item..

The plan is to remove the feed links from all finders, unless we gain
evidence that it is needed. Until this decision is made, we don't want to
introduce the feature for the new licence finder.

A new generalised method could be implented (not use
`is_licence_transaction?`) if we wanted to do this for a subset of
finders, vs all.

The `LiveSearch` module would not be initialised if $atomAutodiscoveryLink returns a falsey value.

Since the subscribe to feed link is removed, this is now an optional argument in `application.js`. The `live_search.js` module is updated to check if `$atomAutodiscoveryLink` is set before trying to interact with it.

…ink is set to null

Since the `$atomAutodiscoveryLink` is now optional, we still want to ensure that all of the existing functionality works as expected.