Additional collapse behaviours for content blocks

For my own project I've modified the contentblocks plugin to have some extra collapse behaviours. The reason for this being that in documents with a large number of content block elements, usability rapidly decreases. 

I've added three more options to the contentblocks plugin that  can be setup in the cluster configuration associated with the contentblock.

• startCollapsed (boolean) - if set to true, the content blocks plugin shows all child elements as collapsed when first shown
• showTitles (boolean) - if set to true, an additional title is included in the header based on the mapping below
• titleMapping (string[]) - an array of strings formatted as `ns:compoundname=ns:fieldname` 

An example of the above as configured in the console:

and the result in the CMS frontend:

I've also attached the diff for the contentblock project, it is only a minor change. I've made the changes in the 14.2.1 version of the plugin, as that was the latest release tag I could find online. 

I could manage the plugin separately, but ideally (if you feel the functionality is appropriate) this behaviour gets merged into the plugin itself.

I'd give permission to release this under the license required by bloomreach.