Committee list page accessible from main menu

[konklone]

A number of people have requested committee search from the main menu, in addition to the per-legislator option we have right now.

• Add an option on the Main Menu to find legislators by Committee.
• When tapped, this will open a new "CommitteeTabs" activity with three tabs, one for "House", "Senate", and "Joint".
• Each tab will list the committees for that chamber. Each tab can be an instance of a new "CommitteeList" activity, that takes a different "chamber" parameter. Each instance of CommitteeList will be backed by one network call to the Sunlight Congress API.
• Each committee, when tapped, will direct to the existing LegislatorList form for a committee search.

Expand CommitteeService to have a new method that gets all committees. You can use this page for documentation of the Sunlight Congress API endpoint that supplies this: http://services.sunlightlabs.com/docs/congressapi/committees.getList/

Try to follow the code patterns set in existing tab activities and network backed lists.

[konklone]

You can leave the new icon to me, I can add that once you're done with the feature.