[Move refactor] Reparent orphan classes (#6236)

* Move orphaned classes to their correct parent folders.

---------

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

cockatrice/src/interface/widgets/utility/line_edit_completer.h

@@ -0,0 +1,35 @@
+/**
+ * @file line_edit_completer.h
+ * @ingroup UI
+ * @brief TODO: Document this.
+ */
+
+#ifndef LINEEDITCOMPLETER_H
+#define LINEEDITCOMPLETER_H
+
+#include "custom_line_edit.h"
+
+#include <QFocusEvent>
+#include <QKeyEvent>
+#include <QStringList>
+
+class LineEditCompleter : public LineEditUnfocusable
+{
+    Q_OBJECT
+private:
+    QString cursorWord(const QString &line) const;
+    QCompleter *c;
+private slots:
+    void insertCompletion(QString);
+
+protected:
+    void keyPressEvent(QKeyEvent *event);
+    void focusOutEvent(QFocusEvent *e);
+
+public:
+    explicit LineEditCompleter(QWidget *parent = nullptr);
+    void setCompleter(QCompleter *);
+    void setCompletionList(QStringList);
+};
+
+#endif