Added support for object groups in the SceneLoader. "groups" is a new property in the SceneLoader result object.

Ex:
input {
  //...
  "objects" : {
    "Object.1" : {
      "groups"    : [ "Group.A" ],
      //...
    },
    "Object.2" : {
      "groups"    : [ "Group.A", "Group.B" ],
      //...
    },
    "Object.3" : {
      "groups"    : [ "Group.B" ],
      //...
    }
  }
}

result {
  //...
  groups: {
    'Group.A': [ 'Object.1', 'Object.2' ],
    'Group.B': [ 'Object.2', 'Object.3' ]
  },
  //...
}
Blender Exporter: I don't think parsing the groups is needed. It exports the objects twice (or more) otherwise.
Blender Exporter: Fixed incorrect JSON when object doesn't have material.
Editor: Show alert() when json fails to parse.
Editor: Support scenes without cameras.
Editor/SceneLoader/SceneExporter: Removed bgColor stuff.
Blender Exporter: Neither is needed to parse the groups here.
Blender Exporter: Missmatch of embed geometry names.
This is the bug I started the day with. And I kept finding other issues on the way. I think it's now fixed, but this made me realise how convoluted this exporter is :(
Ups, returning an alert... It seemed to work though.
Merge remote-tracking branch 'pavelgj/dev' into dev
Removed more SceneLoader bgColor stuff.
SceneLoader: Moved groups handling into a safer place.
Updated builds.