WIP: Resolve "Some database interfaces do not provide access to the annotations stored in the low-level databases"

Closes #14 (closed)

Added a new intermediate biofile and biodatabase interface that stores the low_level file and database objects, and use the annotations function from the low-level database to request the annotations.

I have modified the test cases such that they actually require the annotations to be non-None if the low-level database has internal annotations. These tests will fail unless the database is correctly implemented.

@amohammadi @tiago.pereira @andre.anjos Do you think this is a reasonable way to proceed?