ui: color schemes

Put all colors into single xml file. Accessing colors is handled via the singleton class ColorScheme. The default scheme
"bright.xml" holds the original colors. The scheme "dark.xml" is a start, but still a poor alternative. Color schemes
can be switched via the View menu.

src/app/qt/element/QtCodeFileList.cpp

@@ -14,6 +14,8 @@ QtCodeFileList::QtCodeFileList(QWidget* parent)
 	: QScrollArea(parent)
 	, m_focusedTokenId(0)
 {
+	setObjectName("code_file_list_base");
+
 	m_frame = std::make_shared<QFrame>(this);
 	m_frame->setObjectName("code_file_list");