Save and restore blockly program

[aroberge]

Like text-based programs, it should be possible to save and restore blockly programs. More specifically:

• [x] Save last program run in local storage and make available at next start.
• [x] Enable saving in local storage under a user-defined name
• [x] Enable saving to file
• [x] Enable loading from file

[aroberge]

All done and also added the ability to include blocks configurations in world file.