Improved Media/Image preview in lists.
Styling.
Refactoring.
Fixed loading issues with filters.
Removed log message.
Added following directives:
* `rbs-document-href`: creates a link to a Document in the Backoffice UI
* `rbs-document-popover`: displays a preview of a Document in a Popover. Template for such previews should be located where 'list.twig' and 'editor.twig' are and named 'popover-template.twig'.
Merge pull request #341 from fredericbonjour/Admin

Added `rbs-document-href` and `rbs-document-popover` directives.