icons: include SVG variants of Oxygen icons

The Oxygen license terms state that the preferred modifiable
form (which is SVG) of each icon used in the application must be
distributed, too.

README.md

@@ -336,8 +336,9 @@ safe for those whose name starts with `mkv`.
 
 The preferred form of modification are the SVG icons. These are not
 part of the binary distribution of MKVToolNix, but they are contained
-in the source code in the `icons/svg` sub-directory. You can obtain
-the source code from [the MKVToolNix website](https://mkvtoolnix.download/).
+in the source code in the `icons/scalable` sub-directory. You can
+obtain the source code from the
+[MKVToolNix website](https://mkvtoolnix.download/).
 
   * License: GNU Lesser General Public License v3 (see `doc/licenses/LGPL-3.0.txt`)
   * URL: https://techbase.kde.org/Projects/Oxygen