Refactor the waiting mechanism in the Flex Workflow scenario.

Some behat steps fail occasionally because of timeouts and the driver loosing synchronisation with the web page.
For example:

Given I open :path path in Content Editor
Can't click '...' element: not Found (Exception)

Then I return to Content Editor
Timeout while retreaving DOM element (Exception)

Remarks: Other steps need to be identified.
Note: Memento 1.3!

And I make a modification to :field and send it for review
Timeout while retreaving DOM element. Last exception: Field not found (Exception)

Given I open :path path in Content Editor
Element is no longer attached to the DOM