Add public method to remove a study, given its ID.

@chinchliff , please take a look at this method for removing a study by its ID. This is **untested** code but simple so I hope it's close enough. :dart:

I'm hoping to call this method (from a GitHub webhook script) when a study is deleted from the data repository. If there's already a clean way to do this, please just clobber this branch and let me know.