Fix source editor for the case of no CodeMirror editor.

In the HTML component, there is no longer a tabbed CodeMirror Editor. STUD-1516.

There are no tests for this. I had previously written a smoke test for the high level source editor for LaTeX problems, but it has been disabled because the test did not pass reliably.

In problem-editor.feature:

# Disabled 11/13/2013 after failing in master
  # The screenshot showed that the LaTeX editor had the text "hi",
  # but Selenium timed out waiting for the text to appear.
  # It also caused later tests to fail with "UnexpectedAlertPresent"
  #
  # This feature will work in Firefox only when Firefox is the active window
  # IE will not interact with the high level source in sauce labs
  #@skip_internetexplorer
  #Scenario: High Level source is persisted for LaTeX problem (bug STUD-280)
  #  Given I have created a LaTeX Problem
  #  When I edit and compile the High Level Source
  #  Then my change to the High Level Source is persisted
  #  And when I view the High Level Source I see my changes