Add button icon resource file.

This xpm file is derived from Silk icon set 1.3.

See http://www.famfamfam.com/lab/icons/silk/

This work is licensed under a
Creative Commons Attribution 2.5 License.
http://creativecommons.org/licenses/by/2.5/
update submodule
support to hide folderview on startup
add hide-folderview option