Add favorites / saved bots

[chrisdedman]

Description

Authenticated users can bookmark bots they use or want to evaluate.

Acceptance criteria

• favorite/unfavorite from card/detail page
• /favorites
• duplicate favorites impossible
• favoriting does not affect ranking unless explicitly designed later

[chrisdedman]

UPDATE: Would this feature actually be useful? I am not sure anymore.

If still relevant, it would require adding a new table in the DB for project favorites.