Plane tracks shows the history and the altitude

[liangchen-harold]

I have added a simple track to each of the plane. When one plane is selected, the track will turns colorized, the heighter the plane flew, the more blue it shows :D

preview: http://cs.lcsky.org/wp-content/uploads/2013/07/dump1090_modified.png

[yuvadm]

At the very least, the code needs some formatting and cleanup. But looks good, I'd like to see this merged.

[mindlesstux]

This looks like exactly what I have been pondering for my branch for a few weeks now when I could spare time.

[antirez]

Pretty cool, will review later today after work and merge if everything seems sane.

[wheresalice]

This centers on Milan and doesn't let me drag the map back to where I want it. Great idea, but needs more work for it to be usable for everybody.

[wheresalice]

Actually, it looks like xlinradio is what's broken my ability to drag anything right now. But the centering on Milan still probably wants removing from this commit; if both this and the centering on the first plane seen commit are merged this would work well.

[liangchen-harold]

I fixed some code style issues, and removed a mindless modification on the default zoom level in my original commits. Now the codes looks better, enjoy it:)