Debugger: Use primitive internal widget instead of matplotview

This practically removes any functionality beyond plain plot display,
but does that at least reliably, cross-platform, without dependency
on 3rd party python packages.

Change-Id: Iaff2f78595394522f32264c642df20dd48b83f8b
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

src/plugins/debugger/debuggerprotocol.h

@@ -246,7 +246,8 @@ enum DebuggerDisplay {
     DisplayUtf16String                     = 2,
     DisplayImageFile                       = 3,
     DisplayLatin1String                    = 4,
-    DisplayUtf8String                      = 5
+    DisplayUtf8String                      = 5,
+    DisplayPlotData                        = 6
 };
 // Decode string data as returned by the dumper helpers.
 QString decodeData(const QByteArray &baIn, int encoding);