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/TimeDialog.cpp

@@ -55,14 +55,13 @@ void TimeDialog::PopulateOrExchange(ShuttleGui &S)
          mTimeCtrl = new
             TimeTextCtrl(this,
                          wxID_ANY,
-                         wxT(""),
+                         mFormat,
                          mTime,
                          mRate,
                          wxDefaultPosition,
                          wxDefaultSize,
                          true);
          mTimeCtrl->SetName(mPrompt);
-         mTimeCtrl->SetFormatString(mTimeCtrl->GetBuiltinFormat(mFormat));
          S.AddWindow(mTimeCtrl);
          mTimeCtrl->EnableMenu();
       }