Hierarchical search for stratigraphy

[ollehints]

Users are willing to search for standard chronostratigraphic terms including siblings. For instance, a user would search for Mesozoic, and get also the results where stratigraphy term includes Jurassic.
Thus, the specimen index should include at least one standard chronostratigraphic term and then a hierarchical string (unless there is a better way to construct fast search). Explore how this is achieved in PBDB.