DataSift patchset

This PR contains DataSift's set of patches that we use when browsermob-proxy is distributed with [Storyplayer](http://datasift.github.io/storyplayer), our open-source test automation tool.  We use BMP as a standalone proxy server in conjunction with the Selenium standalone server.  The focus of our changes is on working with BMP exclusively via the built-in REST API.

All changes in this patchset should be completely backwards-compatible with the upstream distribution of BMP; where the changes break b/c, they have to be enabled via the new /features REST API.

* New: pom.xml now builds an executable JAR file too
* New: /features API to discover what a running instance of BMP can do
* New: 'requestLogs' feature to log more information to the console
* New: 'enhancedReplies' feature to wrap API responses in error / success container
* New: additional REST API calls for editing the list of injected request headers
* New: ProxyResource try/catch wrapping to report any unanticipated internal errors back to the BMP client