Allow users to set custom proxy settings in incognito mode.

[Jknapp1208]

Hello Vivaldi community,
I am writing concerning the incognito mode used in vivaldi. I would like to combine the incognito mode with the Tor expert bundle, or alternatively, I2P. There is no way to set a custom proxy for incognito mode without setting a proxy for the entire operating system. Firefox, and its forks have had the ability to set custom proxies seperate from the operating system for years, and if vivaldi had the same feature, it would be the first chromium fork to do so.

[Aaron]

@Jknapp1208
My command line:

vivaldi --proxy-server="socks5://127.0.0.1:1080" --incognito

This should be inherited from chromium.