add environment node support

[Algorush]

I renamed branch but github added changes to the old one. I hope it's okay.
To support loading the envirinment and other nodes, I need to make changes to 3dstreet-editor. Here is the link to the PR with the changes: 3DStreet/3dstreet-editor#195

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[kfarr]

Note to self the testing process is similar to: #287 (comment)

[kfarr]

Hey @Algorush I tested this and it doesn't quite work yet, but I think I made some mistake in not explaining the use case very well. I will try to explain in more detail, here are the desired steps:

• Open up a 3dstreet scene, such as http://localhost:3333/#https://streetmix.net/kfarr/3/example-street (using the testing method linked above)
• Select the environment layer (entity), and then scroll down to the street-environment component
• Change the preset value from day to night
• Save as JSON
• Inspect JSON file on local machine in text editor, expect to see environment entity with street-environment component preset attribute set to night
• Open JSON from 3dstreet and see a night scene
• Instead, what happens with the current version of this PR is that the scene gets brighter -- I think that is because it is adding the lights from the JSON file to the existing lights added by default in the scene

I think there are a few issues here:

• the street-environment component is not listed as a component value to be saved in the json save utils. That should be added, that should be part of this ticket.
• the street-environment component does not support dynamically changing from night into day. It should. This could be a separate ticket. (It is a common problem with a-frame components that they work when initialized once in a scene but need extra work to allow dynamic updating) Here is a separate ticket for this: street-environment component should allow setting after load #303
• we should not save any of the children of the environment id entity (the Environment layer). They should instead be controlled by the street-environment component of the environment id entity. That will probably also need your help to update in json save utils as part of this ticket.

[Algorush]

Thanks for the detailed explanation of how saving the environment should work. I will change it.
In this PR I've made the environment save, taking into account the case if the user will change the light entities directly