[torconnect] Missing a few strings in the DTD

We're missing a few strings in the DTD:

• torConnect.noInternetDescription
• torConnect.finalError
• torConnect.finalErrorDescription
• "Select a Built-In Bridge": I assigned torPreferences.builtinBridgeHeader, but it's already translated as torsettings.useBridges.default with different cases ("Select a built-in bridge")
• torsettings.bridgePlaceholder, which is already translated as torsettings.useBridges.placeholder