add support for SOCKS proxying to support Tor and more

This is not done, but pushed to get your feedback on the approach.

My goal is to, in following your style, not have a "Use Tor" checkbox, but to have the app automatically detect if Orbot is installed and/or running when the user adds an account, and ask the user if they want to use Tor with this account.

In addition, if a user enters a "foo.onion" style Tor address, it would automatically know to route through Tor.

Otherwise, if there is an "advanced" account settings panel at some point, the user could manually set the address to any SOCKS proxy option there.