Create a Play plugin to auto-reconfigure Play apps

The purpose of this pull request is to reduce the amount of rewriting of the Play start script that the buildpack has to perform. Rather than having the Bootstrap wrapper drive auto-configuration, auto-reconfiguration is moved out to a Play plugin. The wrapper is kept in place, but simply delegates to the NettyServer class. So the buildpack should not need changing as it is free to continue to replace NettyServer with Bootstrap in the startup script.

Please note that I have not been able to test this change as I am having problems adding a database service on Cloud Foundry. Mysql failed to connect with a "User ... has exceeded the 'max_user_connections' resource (current value: 4)" wherease Postgres resulted in an opaque error "Configuration error: Configuration error[Cannot connect to database [default]]". I was attempting to push a trivial Play application and specifying a database service via the interactive options on cf push. Note I was using the current cloudfoundry-buildpack-java with the current level of vcap-java support, so I was nowhere near testing this new code. Any instructions for how to test with a database gratefully received!
 
[#52912355]