Bug 115 - Snap-to causes spurious 'toolbar' to appear momentarily at start of dragging.

Completes James' TimeConverter work

This completes the work that James started.  It moves most of the non-GUI
related processing from TimeTextCtrl to James' TimeConverter class.

Other changes include:

1)  TimeTextCtrl now expects the format name instead of the format string to be
passed when creating a new instance.  I found that almost all cases created the
instance with a blank format string and then set the string after creation.

2)  To simplify maintenance and prevent a possible discrepancy between the two,
Increase() and Decrease() were merged into a single routine.

As a result:

1)  All cases where a TimeTextCtrl was being used to extract information and
not actually display a control have been changed to use TimeConverter instead.

2)  All cases where TimeTextCtrl was being created with an empty format and
then immediately followed by something like this:

    tt.SetFormatString(tt.GetBuiltinFormat(c->GetFormat()))

    have been changed to pass the format name instead of the format string when
creating the TimeTextCtrl instance.

src/TrackPanel.h

@@ -22,6 +22,7 @@
 #include "WaveClip.h"
 #include "WaveTrack.h"
 #include "UndoManager.h" //JKC: Included for PUSH_XXX definitions.
+#include "widgets/TimeTextCtrl.h"
 
 class wxMenu;
 class wxRect;
@@ -601,6 +602,8 @@ protected:
    wxInt64 mSnapRight;
    bool mSnapPreferRightEdge;
 
+   TimeConverter mConverter;
+
    Track * mDrawingTrack;          // Keeps track of which track you are drawing on between events cf. HandleDraw()
    int mDrawingTrackTop;           // Keeps track of the top position of the drawing track.
    sampleCount mDrawingStartSample;   // sample of last click-down