Add cobrewers

[danielgtaylor]

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Implement the ability to add other people to a recipe.

[danielgtaylor]

This is slightly more complicated than I thought originally. We need a framework to notify users and request permission to add them to another user's recipe. Each recipe can have a list of approved cobrewers and a list of pending cobrewers (only visible to the recipe author). When a user approves the request they are moved from the pending to the approved list and become visible to all.

Users that are approved on other user's recipes should have those recipes show up in their dashboard and public pages, which means building and index on the recipe's approved cobrewer list.