Add proxy support

[ostkamp]

Hello developers,

I recently did some Java FX training which made use of scenebuilder with a custom library "FontAwesomeIconView" in its videos.

I tried to add that library in office, but found this to be not working. It seems that scenebuilder completely lacks proxy support. Unfortunately in many if not most companies developers have no direct internet access. Access is only possible through a proxy.

I would thus suggest to provide Proxy support to scenebuilder.

I digged deeper into scenebuilder sources, and identified some locations where it needs to be adjusted since using environment variables or Java system properties or even general Maven proxy settings had no effect.

I have added some git patch with hardcoded settings for a server named "someproxy" on port 8080 which does not require any authentication.

This is of course just meant for people that may run into the same situation and require an immediate dirty workaround.

[It works for me (with different server name of course) and in my case I also have to adjust Java cacerts file and add additional certificates since there the proxy also intercepts SSL connections.]

I also changed a search.maven.com URL, since the request on it got stuck.

0001-Added-sample-Proxy-support-hardcoded.patch