Create Collection model

[jaypinho]

A collection will be a group of snapshots (or headlines? possibly both, using polymorphic associations) that a user can share to a permalinked URL.

[jaypinho]

For further development, add fields like the following to the collection_snapshots table:

• "order": to create a slideshow functionality
• "hidden" or "private": to allow certain snapshots to appear only for users with specific access levels
• "caption": self-explanatory

etc.