FIX Host: header handling in proxy mode.

This fixes GH-101 (cross-domain redirects in proxy mode)
and probably some other issues.
move proxy-related code to a better place
TST increase default port waiting timeout to 10s
better handling of hop-by-hop HTTP headers in Splash Proxy Server
TST gzip support for mockserver
FIX an issue with gzip data in proxy mode.

Fixes GH-61. Closes GH-102.
Merge branch 'master' into request-filters-and-logging
TST make use of "mockurl" method in request filters test