Proxysupport for webhooks

[Schwobaland]

It should be possible to set a http-proxy in app.ini for webhooks.
There should be 3 properties:

• HTTP_PROXY
• HTTPS_PROXY
• NO_PROXY

Alternatively env-variables could be used. This would ease the docker-deployment.

[tboerger]

That should already work if your system provides these environment variables?

[Schwobaland]

I tested on MacOS and Windows - and it doesn't work. I think, because of the proxy-property is always overwritten here. In default go-Transport-implementation ProxyFromEnvironment is used.

[lunny]

resolved by #1096