bug correction

[tofitouf]

Too many bugs for the last release, it was time to do something :

• The mysterious Back key : I've just changed the button association. But It's still better to use keyboard, I did added the back menu items. too lazy for the moment. If there are more complains, I'll do it
• The random crash when 2 mfd was opened and closed again.... Quite difficult this one. not to see what happened but the way to correct it was not direct. I needed to change the way data are saved and shared. the good news is that any vessel in the simulation save their mfd states. not only the current one. I added a scenario to the demonstration. it's a cool new feature.

other bugs are :

• trouble when changing of solar system. need to test using MsssMfd ? what's that ? seem cool, I'll try it for fun first.
• Key repeat trouble. old bug.....
• need a better documentation frame alignment are not really clear. (added 2 new png for doc)

Still todo :

• Center on planet and align with a different item (my orbit for instance)
• auto-hide and show menu + animation when disappear.
• auto-scale with a optional period. ( for the moment when a scale is chosen) and if position change (for exemple distance to planet), you've to reselect the scale to take new parameter in account.
• show bases and pads
• show orbit elements for other orbit than current vessel