Campaign gallery

@sergii-tkachenko Can you review?

Refs #3159

* Adds a Campaign Gallery template file, to share between the Campaign Group and Taxonomy Term page templates.

* Refactors Campaign Block vars to call  `node_load` instead of `entity_metadata_wrapper` to avoid Fatal exceptions when fields aren't set.

Pretty sure. This is a copy/paste jam from the `campaign-group.tpl.php`... I don't name the classes :)