Roxterm

Wrapped the GDK_PIXBUF_MODULE_FILE environment variable so that roxterm is able to
load svg files.

Without it I would get the following warnings when starting roxterm:

```
Gtk-WARNING **: Error loading icon from file '/nix/store/36haql12nc3c91jqf0w8nz29zrwxd2gl-roxterm-2.9.4/share/icons/hicolor/scalable/apps/roxterm.svg':
Couldn't recognize the image file format for file '/nix/store/36haql12nc3c91jqf0w8nz29zrwxd2gl-roxterm-2.9.4/share/icons/hicolor/scalable/apps/roxterm.svg'
```

Also added myself as the maintainer for roxterm.