Add support for requiring client certificates

Work remains:
* Remove the client test after fixing it from failing intermittently)
* Verify that the accepting client certificate test no longer fails intermittently
* Add command line configuration option for client certificate
Make test dodge client cert issue

https://issues.apache.org/jira/browse/HTTPCLIENT-1585
Add command line support for client certs
Merge branch 'master' into clientcertwip

Conflicts:
	src/main/java/com/github/tomakehurst/wiremock/core/WireMockConfiguration.java
Fixed broken test in HttpsAcceptanceTest
polish
Added option for keystore password
Added option for truststore password
Added support for proxying to services requiring a client certificate