Get all Collection items

[stuartc]

Re: #2190

Create a Collections module that exposes a function that returns all values for a given collection name.

The result should be a stream of structs containing:

• key : string
• value : map

This is likely the first issue in the epic above, and so we will need some tables.

• collections
  • name (unique)
  • belongs to project
  • timestamps
• collection_items
  • key
  • belongs to project

Acceptance criteria

• Migrations for Collection tables
• A new context module
• A function in the module that returns a stream of items