get ready for new otindex add / update / remove study methods

[kcranston]

In preparation for otindex vs oti, need to modify how we call methods for updating studies. Specifically this code for updating and this code for deleting have hard-coded oti functions. Two options:

1. Modify the phylesystem-api code to call the new otindex functions, and merge / deploy at the same time as otindex
2. Add some config setting that specifies oti or otindex, and then an if statement that calls the appropriate code depending on the index being used

The new functions are v3/studies/add_update and v3/studies/remove and they take either a list of raw github links (same as oti), or simply a list of study ids (shorter!).