Active Proxy Support

Hello,

This PR allows proxy installation, auto registration with server and the means by which Zabbix agents can be associated with a particular proxy at node registration time (or subsequently at node update time). The usage is documented in the README under the Proxy section. I am currently using this with success at my employer and it makes managing many proxies more consistent and migrating agents to a particular proxy can be done automatically.

I realise this is quite a big PR and some of the highlights are

* Only active proxies are currently supported
* Building the proxy and server is almost exactly the same so create common _server_common_build_deps.rb recipe used by both server and the proxy
* Added in some Java gateway fixes (not directly related to proxy but noticed them during testing)
* Determining the correct proxy for a given Zabbix agent to use is something that needs to be figured out in a wrapper cookbook - this is not something we can guess since many companies will have different criteria.
* Only installation of source is currently supported

Tested on Debian and RHEL but more testing "in the wild" needed. 

Any feedback welcome.