add completer interface (item roles)

src/CompletionModelRoles.h

+#pragma once
+
+#include <QAbstractItemModel>
+
+// Interface for completion models
+namespace CompletionModel {
+
+// Start at Qt::UserRole * 2 to prevent clashes
+enum Roles
+{
+        CompletionRole = Qt::UserRole * 2, // The string to replace the active completion
+        SearchRole,                        // String completer uses for search
+};
+
+}