SetAttribute ClickWaitUntilPost WaitUntilNotExists

IWebElementExtension: added SetAttribute, ClickWaitUntilPost,
WaitUntilNotExists
added test for ClickWaitUntilPost
added a new condition ElementAttributeEquals and new wait called
WaitUntilAttributeEquals
Cleanup and document ClickWaitUntilPost
Clean up and documented ClickWaitForPage