Bug 27476: Implement about:torconnect captive portal within Tor Browser

- implements new about:torconnect page as tor-launcher replacement
- adds new torconnect component to browser
- tor process management functionality remains implemented in tor-launcher through the TorProtocolService module
- adds warning/error box to about:preferences#tor when not connected to tor

Bug 40773: Update the about:torconnect frontend page to match additional UI flows.

Bug 41608: Add a toolbar status button and a urlbar "Connect" button.