Fix for bug 3215. All changes in src/frontends/qt4/.

Fix for bug 3215. All changes in src/frontends/qt4/.
Changed dialog and added routines to deal with an "auto" label
in cases where defaults are used.

ui/MarginsUi.ui: Changed labels for width and height to checkboxes. Removed connections.
checkwidgets.[Ch]: Extended checkedLineEdit routines to take a QWidget.
qt_helpers.[Ch]:
  Added void lengthToWidgets(QLineEdit *, LengthCombo *, LyXLength const &, LyXLength::UNIT)
  Added void lengthAutoToWidgets(QLineEdit *, LengthCombo *, LyXLength const &, LyXLength::UNIT)
  Added void setAutoTextCB(QCheckBox *, QLineEdit *, LengthCombo *)
validators.[Ch]:
  Added class LengthAutoValidator : public LengthValidator
  Added class DoubleAutoValidator : public QDoubleValidator
QGraphicsDialog.[Ch]
  Added virtual void setAutoText()
  Added virtual void on_WidthCB_toggled(bool)
  Added virtual void on_HeightCB_toggled(bool)
  Used the new functions to set "auto" in default cases and toggle checkboxes as needed.
  Set validator for scale.
  Re-organized connect routines.
QGraphics.C:
  Completely re-worked update_contents().
  Significant changes to apply().

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@17735 a592a061-630c-0410-9148-cb99ea01b6c8