Issue 5358: Allow pasting HTML into the HTML panel

Steps to reproduce

  1. Open Firebug and switch to the HTML panel
  2. Copy this text: <item id="3">Item Number</item>
  3. In the node tree right-click on the #onlyContent element and select Paste XML > Replace Node
  4. Copy this text: 3
  5. In the node tree right-click on the element with the ID 3 and select Paste XML > Replace Content
  6. Copy this text: <item id="2">2</item>
  7. In the node tree right-click on the <root> element and select Paste XML > As First Child
  8. Copy this text: <item id="4">4</item>
  9. In the node tree right-click on the <root> element and select Paste XML > As Last Child
  10. Copy this text: <item id="1">1</item>
  11. In the node tree right-click on the element with the ID 2 and select Paste XML > Before
  12. Copy this text: <item id="5">5</item>
  13. In the node tree right-click on the element with the ID 4 and select Paste XML > After

Expected result

The iframe should contain this node structure:

<root> <item>1</item> <item>2</item> <item>3</item> <item>4</item> <item>5</item> </root>