Don't assume id for primary key column

[jace]

Several places in HasGeek code including coaster and baseframe refer to self.id or obj.id to retrieve the primary key. This is incorrect usage. The correct method per SQLAlchemy is the following:

from sqlalchemy import inspect
identity = inspect(obj).identity

Note that the identity value here is a tuple and not a scalar as assumed by obj.id.

[jace]

Coaster's use of self.id is currently justified because all usage is within derivatives of IdMixin, which explicitly defines the id column. However, Baseframe's ticket remains valid.

[jace]

Use of self.id has been removed in #112 and #113.