Complete asebahttp integration

Add menu entry for "Web Tools for Thymio" that runs asebahttp with the thymio_motion.aesl file parameter, the default TCP port 3000 (for the HTTP interface), and ser:name=Thymio-II; and asks user's web browser to open the javascript welcome page.

Depends on the following issues in https://github.com/davidjsherman/aseba/milestones/Version%201.4:

davidjsherman/aseba#8
davidjsherman/aseba#7
davidjsherman/aseba#6