Allow user to over-ride link shared with pre-defined entity link.

Re-rolled patch for branch 4.x

We ran into some caching issues with this, where it would not get the new entity (ie page) due to being cached already.

To solve this, moved the logic for doing the preferred link into the preprocess hook, and into its own render array with `#cache => max-age = 0`
As i understand it, it will now always re-render that array into the template. And hence always get the preferred link.
I haven't done anything quite like this before so if that's the wrong approach let me know.

Thanks

Sorry - last patch didn't include the shift of the configuration out of the if statement. This caused a get on null error.
Fixed.

Re-rolling patch updating for version 4.x

Had and issue where the copy link button would copy the original URL not the preferred URL

Update to check field type.

Re-rolled patch for version 4.0.7

Found an issue with this approach, the max-age should not be set to 0, then drupal never caches it.
instead, so we can use caching, set 'contexts' to 'url'.
Not sure if its the right thing to do, as i don't know enough about caching here.