Mac shortcuts shown if appropriate

Detect Mac on User Agent and show Cmd/Ctrl as appropriate
Cmd/Ctrl shortcuts, Ctrl+space added and [?] info

Now showing Cmd or Ctrl after detecting if we're on a Mac from User
Agent
Ctrl+space shown as a shortcut now
[?] added after a couple of shortcuts that require popups to be enabled,
title used as tooltip
cmdKey added as alternative to ctrlKey
cmdKey flag setup & usage

Also slightly taller help screen as Ctrl+space shortcut is added
Also resetKeys on open webpage or get info window