How to use http-proxy for getBrowser & ajax requests? #245

What steps will reproduce the problem?
1. use phpquery for any http(s) request
2. try to configure it using a http(s)-proxy

What is the expected output? What do you see instead?
One should be able to configure an optional proxy-setting just like the setup 
for allowedDomains.

What version of the product are you using? On what operating system?
latest/git

Please provide any additional information below.
It would also be nice being able to get and alter any header/user-agent sent in 
requests.