Loads of changes, fix thread & invoke helpers, skeleton of Core working

* GUIInvoke helper changed to use QMetaObject::invokeMethod which works
  on threads better.
* LambdaThread helper class now has a thread member, it doesn't derive
  from thread (this seems to be recommended practice).

qrenderdoc/Widgets/CustomPaintWidget.cpp

@@ -3,10 +3,9 @@
 
 #include "renderdoc_replay.h"
 
-extern ReplayOutput *out;
-
 CustomPaintWidget::CustomPaintWidget(QWidget *parent) : QWidget(parent)
 {
+  m_Output = NULL;
   setAttribute(Qt::WA_PaintOnScreen);
 }
 
@@ -17,6 +16,6 @@ CustomPaintWidget::~CustomPaintWidget()
 
 void CustomPaintWidget::paintEvent(QPaintEvent *e)
 {
-  ReplayOutput_Display(out);
+  if(m_Output) m_Output->Display();
 }