GH-903 simple theme switching and dark theme

application/themes/ITheme.h

@@ -0,0 +1,13 @@
+#pragma once
+#include <QString>
+#include <QPalette>
+
+class ITheme
+{
+public:
+	virtual ~ITheme() {}
+	virtual QString id() = 0;
+	virtual QString name() = 0;
+	virtual QString appStyleSheet() = 0;
+	virtual QPalette colorScheme() = 0;
+};