Hack at Media Model to store ID when loading Media, make props public

* Needs refinement, but this is fine for view refactoring.
Abstract "Preview Block" into a partial based on a Media object.

* This is the ultimate end goal, and the "preview block" is used in
  multiple places in the application.
* The Controllers now only grab the IDs, trusting Media::getByID() to
  load the correct model using the ID.
  * Prime for refactoring into a model method.