Make poses easier to specify in yaml files

[analog-cbarber]

1. I find it tedious when manually building a world file to have to compute absolute
   world coordinates for locations and objects. It would be nice if those could be
   specified relative to the parent's center point. (Allow specifying poses relative to other locations #298)

2. Another annoyance is the use of radians for pose angles. Degrees would be much
   more user friendly for text formats. (Allow use of radians or degrees for angle units in poses #300)

3. Would be nice to be able to specify colors as strings supporting standard color strings like "red" or "#0F0F0F".
   (that goes for the API as well) (Allow color specification in non-RGB formats #301)

4. Would be nice if multiple sources of location/object metadata could be included (Allow supporting multiple sources of object/location metadata #299)

[sea-bass]

I like these suggestions -- thanks for writing them down here!

The only one I may push back on is the use of degrees. If anything, it should be an option, which still maintains radians as the default.

But generally, the "pose from YAML" capabilities could be improved beyond just loading from a vector whose length dictates the pose format.