Introduce `servers`

[LukeBrandon]

Servers are a place for people to hangout and share info

Servers have the following behavior:

• Channels can belong to servers (if they don't, its a DM)
• Users can be added or removed from servers
• Channels can be listed for a server

[LukeBrandon]

@LukeBrandon To isolate and enumerate the other urls and models we need to make this happen