Auto version

The VERSION static field in the Deproxy class had been hard coded. This led to the User-Agent header (added by the DefaultClientConnector) and the Server header (added by DeproxyEndpoint) having the wrong version, because we forgot to update the VERSION field in previous releases.

This pull request changes how the VERSION field is populated. Instead of it being hard-coded, the value is automatically pulled from a resource file that hase the version number from the pom injected into it. Header values are now correct. There is now only one place that we need to change the version number in subsequent releases.