Add an option to send GlobalPrivacyControl's Do-Not-Sell signal to Stealth Mode

[ameshkov]

More on Global Privacy Control:

• https://globalprivacycontrol.org/
• Reference implementation: https://global-privacy-control.glitch.me/

Actually, we'll unite "Do-Not-Track" and "Global Privacy Control" in a single setting.

Implementation

When this option is enabled, we should do two things in addition to what we did for Do-Not-Track:

1. Send a DOM signal: see here
2. Send an HTTP header signal: see here (Sec-GPC header with value 1)

Client app changes

We should mention this in CoreLibs changelog:

Client applications must rename "Do-Not-Track" to
* Name: Send websites signals to not track you
* Description: Send the "Global Privacy Control" and "Do-Not-Track" signals to the websites you are visiting

[TPS]

Reading the above, the single setting controls both "Do Not [Track, Sell]", but the (AGA, @ least) UI option (setting, log entry) only says the 1st. Could that be clarified?