Move some variables into const.hpp

Clean up some code in the AccountManager

src/const.hpp

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <QString>
+
+namespace chatterino {
+
+static const QString ANONYMOUS_USERNAME_LABEL(" - anonymous - ");
+
+namespace twitch {
+
+static const QString ANONYMOUS_USERNAME("justinfan64537");
+
+}  // namespace twitch
+
+}  // namespace chatterino