Add unit tests for world knowledge utilities

[Sebastian Castro]

The world knowledge utilities, found at pyrobosim/pyrobosim/utils/knowledge.py, could use some unit testing.

These utilities perform several fundamental tasks used throughout pyrobosim, particularly for locating world entities (rooms, locations, objects, robot, etc.) given a world object and its corresponding location/object metadata.

These functions can be quite complex in that they need to convert generic queries (e.g., "kitchen apple") into specific instances, or lack thereof. As such, getting this functionality right has significant impact on the rest of pyrobosim.

[Henry Moore]

I'm going to work on this