Add Post Model

[siman4457]

This issue is tied to a couple open issues on OpenTacos:

• Get additional details for RecentMedia component #583
• Photo descriptions #498

In order to address the above tasks, we need to combine the actions of a new upload and an item on the "recent tag" page. The product is something called a "post".

UI flow:

1. User selects one or more photos to upload
2. User adds an optional description for the overall post
3. User is prompted to add at least one tag on each uploaded photo
4. User submits a new post

Changes to the current model:

• Rename the current media collection to "tags"
• Create a migration script to move data from media collection to the new tag collection. Consider using something like migrate-mongo
• Rename Schema, Model, Types, etc for media collection to tags in openbeta-graphql

[vnugent]

Rename the current media collection to "tags"

If it's easier to maintain existing tagging functionality while this new feature is under development, can we call the new media collection MediaX or something like that?