TLS fingerprints (2.1)

  -  [x] Write tests
  -  [x] Wait for https://github.com/shazow/urllib3/pull/444
  -  [x] Wait for https://github.com/mitsuhiko/werkzeug/pull/565 -- use git version
  -  [x] Wait for kennethreitz/requests#2192 -- [worked around it](https://github.com/vdirsyncer/owncloud-testserver/commit/6499b760d9550e68366202e1c35f93f2ede48a44)