Sample Projects

## Not ready to be merged

This PR adds support in Codebox and Codebox.io for sample projects:

- If command line tool is run with ```--sample=node```: it will replace workspace content with a sample
- (to finish) init.sh for codebox.io check if no git (and not hg) and use --sample=$CODEBOXIO_STACK
- (to do) Menu file has now a submenu "Samples" to replace content with a sample from a list