save / load - support environment node

[kfarr]

save environment node in 3dstreet json and support loading of it

• the environment entity has "street-environment" component - it will save day or night as part of the component property. that is the only thing we need to save at the moment.
• do not save any children of environment component such as lights or sky, they should be generated dynamically based on the street-environment component

[Algorush]

#300

[kfarr]

#303 is a blocker to be done prior to this ticket 292 being possible to complete

[kfarr]

closed by #300 and #303