Add new TrPathButton class (Qt client)

Make use of new button class in torrent options dialog.
Rework Utils::removeTrailingDirSeparator to return correct value for "/".

qt/path-button.h

@@ -0,0 +1,56 @@
+/*
+ * This file Copyright (C) 2014 Mnemosyne LLC
+ *
+ * It may be used under the GNU GPL versions 2 or 3
+ * or any future license endorsed by Mnemosyne LLC.
+ *
+ * $Id$
+ */
+
+#ifndef QTR_PATH_BUTTON_H
+#define QTR_PATH_BUTTON_H
+
+#include <QToolButton>
+
+class TrPathButton: public QToolButton
+{
+    Q_OBJECT
+
+  public:
+    enum Mode
+    {
+      DirectoryMode,
+      FileMode
+    };
+
+  public:
+    TrPathButton (QWidget * parent = nullptr);
+
+    void setMode (Mode mode);
+    void setTitle (const QString& title);
+    void setNameFilter (const QString& nameFilter);
+
+    void setPath (const QString& path);
+    const QString& path () const;
+
+  signals:
+    void pathChanged (const QString& path);
+
+  private slots:
+    void onClicked ();
+    void onFileSelected (const QString& path);
+
+  private:
+    void updateAppearance ();
+
+    bool isDirMode () const;
+    QString effectiveTitle () const;
+
+  private:
+    Mode myMode;
+    QString myTitle;
+    QString myNameFilter;
+    QString myPath;
+};
+
+#endif // QTR_PATH_BUTTON_H