Rjwebb/conversations list uses summary endpoint

[rjwebb]

This PR adds a new endpoint GET /api/v3/conversations_summary which returns a list of the conversations with only the fields returned that we need for the "Manage Conversation" and Dashboard conversation lists. It also includes the UI changes needed for that. This includes a new reducer conversations_summary.

Some more changes:

• The list of conversations and the filter buttons in the dashboard now live in a separate component ConversationsList
• After moderating a conversation, the conversation list is updated
• The single conversation view on the Dashboard uses zid_metadata
• Redirect to dashboard main page if conversation cannot be found (e.g. broken link)

[raykyri]

Looks good to me