Rework the filebrowser some to add some functionality. A "hidden" preference now...

Rework the filebrowser some to add some functionality.  A "hidden" preference now stores the default directory to open.  This directory is marked with a gold star.  To change the default directory, you touch on a star.  Added icon for directories.  Added preference to control if only ork files are shown in the file browser.  Changed the sort order to do the fancy "logical" sort to compare number components numerically.

git-svn-id: https://openrocket.svn.sourceforge.net/svnroot/openrocket/trunk@415 180e2498-e6e9-4542-8430-84ac67f01cd8