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/chatwidgetheader.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "signallabel.hpp"
+#include "widgets/basewidget.hpp"
 #include "widgets/chatwidgetheaderbutton.hpp"
 
 #include <QAction>
@@ -13,10 +14,14 @@
 #include <QWidget>
 
 namespace chatterino {
+
+class ColorScheme;
+
 namespace widgets {
+
 class ChatWidget;
 
-class ChatWidgetHeader : public QWidget
+class ChatWidgetHeader : public BaseWidget
 {
     Q_OBJECT