--replay-ignore-content & --replay-ignore-param ported from branch 0.10

Hi!
As talked in pull request https://github.com/mitmproxy/mitmproxy/pull/368 I've ported changes to master. 
for now only  replay-ignore-content and replay-ignore-param were ported as no functionality changed. 
It will take more time to rewire kill for use filters, so i've split changes and worked on this two first.
Regards.
Marcelo