able to see all moons

added the ability to see which faces have been flown over on all moons.
mass calculation and arc colouring added

The most recent leg arc is now coloured depending on the dv for that leg
of the tour. Green when dv <5, yellow when dv<200 and red otherwise.
Previous legs are also coloured grey.

Also the mass of the spacecraft is now calculated after each DSM.
some comments and duplicate code removed
Minor improvements and code clean-up

moved gui.busy out of main.html. created a webGL check which redirects
the user to a troubleshooting page in case of errors. Added simple
instructions for the user.
Update to THREE r.58
controls changed as to accomodate a minimum zoom, a maximum zoom
Moon Names Added as sprite elements
color and style change of instructions
moon name sprite work finished ....
Sprite code moved into elements.js (refactoring)
Info translucent window created and 'walk through guide' system set.

JQuery is now needed as external library
jQuery stuff moved locally