Blacklist with method matcher

[neoalienson]

Added new parameter 'method' for blacklisting. Useful in simulating 500 on CORS APIs, where OPTIONS should not be blacklisted. e.g.,
curl -X PUT http://localhost:8080/proxy/[:port]/blacklist -d "regex=.*&status=500&method=POST"

[jekh]

I know this has been merged already, but could you add some unit tests for this feature? That will make it easier to verify whether other changes to the blacklist have broken this functionality.

Also, FYI -- when I merged this branch into PR #126, I re-added the blacklistRequests(String pattern, int responseCode) method to ProxyServer. All existing client code that blacklists requests from within a Selenium test uses this method, so it would be a breaking change to modify its signature.