CoeSwd6: User Def Axis Units: Replaced ScaledUnitPtr with new AxisUnitInfo class
Bug Number: n/a
Release notes (y/n): no
For Release Nums: 7.1

In the prior commit, the axes unit strings were replaced with a ScaledUnitPtr 
-- with logic changes to map all slots having the same UNIT TYPE of an axes' 
ScaleUnitPtr to that axes.  This applied to both Sim/PlotInfo (class AxisInfo) 
and Q3GUI/SlotPlot (class SlotPlot::AxisItem).

This commit replaces those ScaleUnitPtr fields with a new class, AxisUnitInfo 
(in Sim/PlotInfo) which provides a switch between a ScaledUnitPtr determined 
from the first slot added to that axis AND a custom ("fixed") scale and unit 
configuration. 

NOT YET implemented:

(1) AxisUnitInfo serialization. (This will be a small XML record, 
    similar to other new support classes in PlotInfo)

(2) Enhancements to the AxisDlg to edit values in the AxisUnitInfo object.


//----------------------------------------
class AxisUnitInfo
{
 public:
   typedef enum
   {
     UnitMode_Slots = 0, // units of first slot added to axis
     UnitMode_Fixed      // specified scale and units
   } UnitMode;

 private:
   UnitMode _unitMode;
   unit_type _unitType;
   ScaledUnitPtr _firstSlotUnits;  // may be NULL, not persistent
   ScaledUnitPtr _fixedUnits;      // may be NULL

 public:
   AxisUnitInfo()
    : _unitMode (UnitMode_Slots),
      _unitType (NUMUNITS),
      _firstSlotUnits (NULL),
      _fixedUnits (NULL) {}

   bool operator== (const AxisUnitInfo& rhs) const;
   bool isDefined() const { return (_unitType != NUMUNITS); }
   void clear();

   UnitMode unitMode()     const { return _unitMode; }
   bool unitMode_isSlots() const { return _unitMode == UnitMode_Slots; }
   bool unitMode_isFixed() const { return _unitMode == UnitMode_Fixed; }

   unit_type unitType()           const { return _unitType; }
   QString unitTypeStr()          const;
   ScaledUnitPtr firstSlotUnits() const { return _firstSlotUnits; }
   ScaledUnitPtr fixedUnits()     const { return _fixedUnits; }

   void setUnitMode (UnitMode);
   void initialize (ScaledUnitPtr);
   bool setFirstSlotUnits (ScaledUnitPtr); // return indicates change
   bool setFixedUnits (ScaledUnitPtr);     // return indicates change

   ScaledUnitPtr activeUnits() const;
};
//----------------------------------------