A lot of changes

Remove unused constructor of messages::Message
Fixed LimitedQueueSnapshot _-prefixes
Changed LimitedQueueSnapshot's usage of int to std::size_t
ColorScheme is no longer a singleton
Created a "BaseWidget" class which is pretty much a QWidget except it
has a reference of ColorScheme since most widgets will need a reference
to the style they should use.
BaseWidget can be implemented either with a BaseWidget parent (which
will copy the ColorScheme reference from the parent) or with a
normal QWidget parent and an explicit ColorScheme reference.
Save main window geometry on close
Fix font changing in the Settings Dialog
Update settings library version

src/widgets/notebookbutton.hpp

@@ -18,7 +18,7 @@ public:
 
     int icon = 0;
 
-    NotebookButton(QWidget *parent);
+    NotebookButton(BaseWidget *parent);
 
 protected:
     void paintEvent(QPaintEvent *) override;
@@ -28,9 +28,9 @@ signals:
     void clicked();
 
 private:
-    bool _mouseOver = false;
-    bool _mouseDown = false;
-    QPoint _mousePos;
+    bool mouseOver = false;
+    bool mouseDown = false;
+    QPoint mousePos;
 };
 
 }  // namespace widgets