MNT-17527 Add support for annotation layer

[yregaieg]

In order to have clickable links in PDFJS viewer in Alfresco Share, the annotation layer needs to be rendered. In this PR, I added the support for this feature and added an activation flag (defaulting to true) as discussed with @esplinr. Alfresco can switch that back to false by default and have a config entry (in share-config-custom.xml for instance) defining that setting. IMHO it should be active by default (as it was with the swf previews back in 4.x) and customers can opt out of the feature by a simple extension setting the activation flag to false.

[davidcognite]

Thanks for the PR! As referenced in the title, we've already got an MNT ticket for this: https://issues.alfresco.com/jira/browse/MNT-17527 - so will continue the discussion there about getting this fix reviewed and merged.