Move internal classes QmlJSEditorEditable/SemanticHighlighter
out of qmljseditor.h. Move QmlJSEditor from namespace
QmlJSEditor::Internal to QmlJSEditor.

Reviewed-by: Christian Kamm <christian.d.kamm@nokia.com>

This only works when a qmlviewer is in the PATH, which is non obvious.
Removing the feature therefore completely.

An error dialog would be more explicit, but too late because of string
freeze.

This was needed since we cannot start stuff otherwise without a project

Task-number: BAUHAUS-450
Reviewed-by: kkoehne