Templates for Engines

[rickybanister]

We will be adding designs to this ticket, but for tracking purposes, it's here now.

We would like to implement optional templates for engines. The option will display in the same place as the cms template dropdown, after you've selected a certain engine. If there is only the default template the dropdown will disappear.

We will use these when we need two different views of blog posts, or two engines are used on a site for two distinct purposes (news and press releases, etc.). It would also be useful for the media plugin to have a photo/video media engine with a view-centric template. And a second template for other files (doc, ppt) more focused on the metadata and file sharing.