Initial work to support Tor (Orbot) and proxying

He there. I am with the https://guardianproject.info and we like Lightning alot. This PR is for the most basic integration of support for proxying Lightning's webviews through Tor, but it does work. It could be expanded to be a general preference, and include support for other HTTP proxy servers if desired.

Otherwise, we would like to explore adding more privacy-by-default options into Lightning, perhaps make Incognito actually secure/privacy, support encrypted bookmarks, downloads, and more. If you are interested, we'll keep sending PR's, otherwise we can also fork. Up to you!

Regardless, keep up the great work on a nice app!