allow to set a general Proxy in the admin.

Estimate: 18h

Does the effort for this relate to JVM proxy parameters not working with lucee/tomcat ?

https://groups.google.com/forum/#!topic/railo/v76mpciogU8
https://dev.lucee.org/t/webservice-debug-set-up-fiddler-for-lucee/1455

PR to fix and add this to the Administrator
https://github.com/lucee/Lucee/pull/769

If you configure a non existent proxy server, the admin update and extensions pages show no content, so it seems to be working

this is covered by LDEV-1114