add leadership for the 116th Congress

[JoshData]

This PR adds leadership from https://www.house.gov/leadership and http://www.senate.gov/senators/leadership.htm. Fixes #654.

I changed the way titles were done in the past: Titles now all have "House" or "Senate" in them so that the title can be fully understood without knowing the context of the relevant chamber. So, where we had Minority Leader before, this PR makes it House/Senate Minority Leader, which I think is clearer and more accurate since this data is typically displayed in applications that show information for Congress as a whole rather than just one chamber. I went back to historical leadership data and updated those titles to match as well.

I assumed all of the roles started on Jan 3 --- not sure if that's true.

I also made some changes to the official titles e.g. replacing the party in the top titles with Majority or Minority because this is how they are generally referred to, and otherwise they'd be inconsistent. I also changed Chairman/Chairwoman to Chair to avoid promoting gendered roles.

Here's the complete set of new data:

Name	Official Title	Title in this Pull Request
Grassley	President Pro Tempore	President Pro Tempore of the Senate
McConnell	Republican Leader	Senate Majority Leader
Thune	Assistant Republican Leader	Assistant Senate Majority Leader
Barrasso	Republican Conference Chairman	Senate Republican Conference Chair
Ernst	Vice Chairman of the Senate Republican Conference	Senate Republican Conference Vice Chair
Blunt	Republican Policy Committee Chairman	Senate Republican Policy Committee Chair
Schumer	Democratic Leader / Chairman of the Conference	Senate Minority Leader
Durbin	Whip	Senate Minority Whip
Murray	Assistant Democratic Leader	Assistant Senate Minority Leader
Stabenow	Chairwoman of Policy & Communications Committee	Senate Democratic Policy & Communications Committee Chair
Klobuchar	Chair of Steering Committee	Senate Democratic Steering Committee Chair
Pelosi	Speaker of the House	Speaker of the House
Hoyer	Majority Leader	House Majority Leader
Clyburn	Majority Whip	House Majority Whip
Lujan	Assistant Speaker	Assistant Speaker of the House
Jeffries	Democratic Caucus Chairman	House Democratic Caucus Chair
McCarthy	Republican Leader	House Minority Leader
Scalise	Republican Whip	House Minority Whip
Cheney	Republican Conference Chairman	House Republican Conference Chair
Palmer	Republican Policy Committee Chairman	House Republican Policy Committee Chair

[dwillis]

Ok by me.