Provide a toggle for Upgrade‑Insecure‑Requests in the control panel

[ExE-Boss]

Right now, when a HTTPS site which has HTTP only resources is loaded, the only way to disable Upgrade-⁠Insecure-⁠Requests is to go into the options, which takes more time than just flipping a toggle in the popup control panel.

[KrasnayaPloshchad]

There is MixedContentHunter extension made for this, but it would be nice if Smart HTTPS can make better implememtation.