Add optional `uri` argument for LoadJSON and add ReadRobotJSON and ReadKinBodyJSON

[superfashi]

This PR adds optional uri argument for LoadJSON.

It also adds ReadRobotJSON and ReadKinBodyJSON for completion.

[rdiankov]

The mechanics of ReadRobotJSON and ReadKinBodyJSON are not consistent with the other Read functions. For some reason, your implementation requires the parts to be already added to the environment.

[rdiankov]

The mechanics of ReadRobotJSON and ReadKinBodyJSON are not consistent with the other Read functions. For some reason, your implementation requires the parts to be already added to the environment.

Particularly, why is the following code necessary if the body is not in the environment:

+            FOREACH(itviewer, _listViewers) {
+                (*itviewer)->RemoveKinBody(robot);
+            }

[superfashi]

The mechanics of ReadRobotJSON and ReadKinBodyJSON are not consistent with the other Read functions. For some reason, your implementation requires the parts to be already added to the environment.

Particularly, why is the following code necessary if the body is not in the environment:

+            FOREACH(itviewer, _listViewers) {
+                (*itviewer)->RemoveKinBody(robot);
+            }

This part of code I just simply copied from other Read[Type] functions. https://github.com/rdiankov/openrave/blame/production/src/libopenrave-core/environment-core.h#L1747-L1757

About the implementation requires the parts to be already added to the environment, that should not be true. I tested and it can parse with empty environment.

[rdiankov]

@superfashi if uri is empty, did you test that the loaded objec'ts GetURI returns just "#XXX"?

[rdiankov]

thanks~