Add list and count videos by folder on CMS

[brunapimenta]

Nowadays users are only able to list and count videos by an account. Giving them the ability to filter by folders could help improving the process by syncing/importing only desired videos instead of all the existing videos in an account.

e.g. Using one Brightcove account for an organization with hundreds of small sites each with a hundred or so videos. The current solution means that each site with only a hundred or so videos must sync all videos in the organization (thousands) even though it only uses a hundred. Separating them by folder would help and, then, the Drupal module on each site could be configured to only sync specific folders instead of all videos.

More examples can be found here.

Closes #47

[firewaller]

This is very helpful, would love to see it get merged in.