Review some dialogs - Githubissues

[ ] Instead of reusing the print-html window, help() should get a dedicated window, whose content is never automatically erased.
[ ] help with no argument should display reeborg_xx instead of just the list of commands as it does now.
[ ] print, and similar windows should be closed automatically when a world is reloaded (but they should be reinitialized, to appear at the correct default location)
[x] There should be a function to open World Info if it is not open already, and leave it open otherwise; this could be used to give instructions -- implemented as RUR.show_description().

aroberge / reeborg