Adding buoy model with textures

[jmf]

I have made a navigation buoy. The Idea was inspired by the buoys in oolite, the model is completely new.
Screenshot:

• Buoy in the red blinking phase
  
• Buoy in the green blinking phase
  

[robn]

I like this very much. Unfortunately right now we have no code that can make use of it, so I will hold this PR open until such time as we do.

[ecraven]

Could we use this in front of station entrances, to help with aligning correctly?

[fluffyfreak]

That might be a good idea, or to identify queuing locations outside stations.

[ghost]

We'll have to make sure the position of the queue (or buoy) is outside of the current launch path. That is the biggest problem right now with increasing traffic - ships landing and starting are crashing into each other (as well as ships lining up to land crash into other ships waiting to land).

I think nozmajner also made a nice buoy model a few months back when I wanted to include in the SAR missions (got voted down though - with good reason).

[nozmajner]

Shouldn't these kind of designators be UI only? I mean it feels strange to put a bouy anywhere, could easily become a navigational hazard. Like if balloons would designate parts of an airport.

[nozmajner]

Don't know if this is needed right now. Will repoen, if/when so.