Attempt to fix #81.

The idea is to tell opened windows (such as tabs) from child windows (such as iframes), because opened windows have their own top.

Consider a few scenarios:

Normal single app load

• App loads
• Snow attempts to apply first protection (to top)
  • Trying to set mark
    • No mark
      • Mark and protect
    • Marked
      • Since this is a top window, warn user that the page is probably compromised and bail on protection - this really should never happen, only if something malicious ran before SNOW

App load + iframe

• App loads
• Snow protects top
• Attacker opens iframe
  • Trying to set mark
    • No mark
      • Mark and protect
    • Marked
      • Since this is NOT a top window, apply infinite loop and DoS page because only attacker can cause this
  • Snow instance in iframe loads
    • Snow protection is called
    • Since window is not top, Snow bails
      • Safe because top already protected iframe when created
        • PROBLEM TO FIX: If some inner page applies different Snow protection than upper page, it will be ignored by Snow!
          • ALSO: Is this problem relevant to next scenario as well?

App load + open window

• App loads
• Snow protects top
• Attacker opens tab
  • Trying to set mark
    • No mark
      • Mark and protect
    • Marked
      • Since this is a top window, but it is also being protected by opener Snow, tell user Snow bails and that it's ok
  • Snow instance in opened tab loads
    • Snow protection is called
    • Trying to set mark
      • No mark
        • Mark and protect
      • Marked
        • Will fail to set mark because opener already marked
        • Since window is in fact a top, bail on mark attempt, we trust opener has set protection