Add "morphologies" as association method among all vertebrae, ribs and in bone group creation

[lfkennedy]

It would be nice if it were possible to automatically associate bones that were added as a bone group that do not directly articulate. Currently, "morphologies" is present as an association type, and would be a way that vertebrae from a single vertebral column and/or ribs from a single rib cage could be associated. This association method is not currently added to the vertebrae or ribs.

This request is therefore two parts:

1. add "morphologies" as a possible association method among all vertebrae and among all ribs
2. add ability to select association method for bone group when it is being added

This would be helpful because it would more concretely tie together these elements. For example, if I have cervical vertebra 6, thoracic vertebra 1, and thoracic vertebra 3 or 4, I may be reasonably sure that these vertebrae are all part of the same vertebral column, particularly if I am inventorying an accession without commingling. Similarly, seriated ribs “nest” together and are similar in size and morphology and can be grouped together as a result. The appropriate way to associate these bones with each other would be through "morphologies" as they do not directly articulate.

The second part would mean that we could select the appropriate association type as an indication of why we are adding all elements as a bone group that we would like to have show up as a skeletal unit likely associated with one individual.