Relational and View Diagram dialog refactoring

* The child actions for relational and view diagrams create dialogs from
  classes that duplicate the same functionality. This refactors the classes
  so that only one class displays the dialog and its factories are
  replaced with diagram models that provide the small differences in
  functionality.

* [*]Action
 * The dialog requires a dialog model which encapsulates both the relational
   object and selected file

* Dialog updates
 * Icons for description and sql tabs
 * Help text is moved from the main panel to the message area of the dialog

* [*]Panel
 * Extends the use of the abstract parent class to reduce code duplication
 * The dialog model is passed in as the container for the reference and
   model file
 * Replacement of GridData and GridLayout instances with the use of
   GridDataFactory and GridLayoutFactory
 * Removes all use of hint heights to address the specific sizing issue.
   Neither the tab folder nor the name text components have priority over
   the sizing.
 * Removes spacers to reduce real-estate requirements of dialogs