Add support for proxying over Tor/Orbot

[n8fr8]

Seems like you have the basic localhost:8118 proxy support in already. Let's talk about what further tuning might be needed.

[mpodroid]

GLDroid only does HTTP requests through android HttpClient.
Is proxy enough to protect network traffic? Do we need something else/more?

[n8fr8]

There is risk of DNS leakage with HTTP, so using a properly configured SOCKS proxy with remote DNS resolution can handle that.

In addition, if the traffic is going to exit Tor, then it will need to be tested with HTTPS.

[hellais]

I think we should either only allow GLDroid to run over Tor or perform a check to see if OrBot is installed and if it isn't display a big fat disclaimer warning the user of the possible issues of not using Tor.
He should agree to this disclaimer and possibly display it every time until he installs OrBot.