Break up Civic Hackers, Script CFA Updating

This pull request

1. Breaks up the long list of "Civic Hackers" with groups for Code for America and Open Knowledge Foundation

2. Adds a small `script/fetch-cfa` to update the list of known brigade orgs via the CfA API

Questions:

1. Any other large groupings worth breaking up?

2. Are these all the brigades? Are we using the API properly?

/cc @ashleymmeyers for the excellent idea (and @jlord because CFA :smile:)