Org pages in addition to team pages

[carols10cents]

Right now, we have teams stored as orgname:teamname, and you can only visit crates for that team. What might be more important than teams is organization, especially because github doesn't always surface teams in their UI.

For example, crates.io knows about these teams:

• https://crates.io/teams/github:rust-lang:libs
• https://crates.io/teams/github:rust-lang:regex
• https://crates.io/teams/github:rust-lang:log
• https://crates.io/teams/github:rust-lang:core
• https://crates.io/teams/github:rust-lang:crates-io-pushers

As a user looking for a crate, I care more about the crates being in the rust-lang organization more than I care about the crates being owned by any of the teams.