Leftover OID -> ID changes

A while ago, we decided that 'oid' is only appropriate when talking about the datatype, and function names should have 'id' when talking about an object's id.

While moving the python bindings to use this, I noticed that we still have some functions and structs using the old naming, so I wend and changed it so we now only expose 'id' there.

The changes are mostly mechanical (`M-x replace-string` is your friend) and hopefully don't conflict too much with anybody's changes.