Collections MVP

[RunDevelopment]

Closes #266

I quickly put together an MVP for collections. A collection is a list of models with a name, description, and author. Each collection has its own page like this:

Collections are linked to by the models they contain and on their authors' pages:

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TODO:

• Improve the design of collection cards. They are too similar to model cards. I want to eventually show collections on the home page, so they need to be visually distinct.
• Add a way to add collections.
• Add a way to add/remove/reorder models in collections.

[joeyballentine]

Are those TODOs for this PR or just future work? I haven't reviewed this yet because I thought you still had work to do on it

[RunDevelopment]

Sorry, it took a while. I resolved all TODOs.

[joeyballentine]

LGTM, thanks for the hard work 👍