OutOfBodyExperience - removing IFrame from body

For foreverFrame transport SignalR appended the iframe as the last child of the body node. However some libraries (e.g. jQuery UI) move nodes inside the body which causes the iframe to reload which results in sending a "connect" request even though the transport has already been started. Because we cleaned up some things after sending the original "connect" request the second "connect" request may cause "Object expected" exceptions. The fix is to move the iframe outside the document body node so it is less likely to be touched/moved by the user's code.

Fixes #2795
Merge branch 'bug-2795' into dev