Added autocomplete for first_for_patient()/last_for_patient()

[rw251]

This is still a work in progress. We still need to add some sort of way of checking that the things in ./patient_level_table_definitions match 1-2-1 with the EventFrame tables.

• could be a check in the @table property, but would need some gymnastics to exclude things like tables created in tests
• maybe better as a test
• would need to exclude things like tpp.medications which extends from core.medications (rather than EventFrame) and adds a column. This doesn't work with the existing implementation. Could be added in future.
• maybe the just update-patient-level-table-definitions could be part of the devenv command so it would get called e.g. when tests were run