Remove unnecessary InstanceMethods module.

In ActiveSupport 3.2, use of this module is deprecated. Since methods
in the Concern module are already available on instances when the
module is mixed into a class, we can just shift the contents of
the InstanceMethods module up to the Concern module.
set_table_name is deprecated in Rails 3.2.
Name NcsCodedAttribute extensions modules.

Added while troubleshooting a Rails 3.2 issue. Turned out that the
problem was elsewhere, but this is a useful change for future debugging
and matches with the behavior of ActiveRecord in 3.2 (cf.
`SomeModel::GeneratedFeatureMethods`).
ActiveRecord 3.2 uses AR::Base.inherited.

This means it's necessary to call the replaced method which we
weren't doing before.