GH-378 add basic custom theme support

Files you can customize are created in themes/custom/

application/themes/CustomTheme.h

@@ -0,0 +1,28 @@
+#pragma once
+
+#include "ITheme.h"
+
+class CustomTheme: public ITheme
+{
+public:
+	CustomTheme(ITheme * baseTheme, QString folder);
+	virtual ~CustomTheme() {}
+
+	QString id() override;
+	QString name() override;
+	QString appStyleSheet() override;
+	QPalette colorScheme() override;
+	double fadeAmount() override;
+	QColor fadeColor() override;
+	QString qtTheme() override;
+
+private: /* data */
+	QPalette m_palette;
+	QColor m_fadeColor;
+	double m_fadeAmount;
+	QString m_styleSheet;
+	QString m_name;
+	QString m_id;
+	QString m_widgets;
+};
+