If one declares a new Database with the name `Database`, then Sphinx cannot compile the documentation

For some reason, Sphinx has trouble swallowing a database declared in this package (or a dependent one) with the name Database.

Steps to reproduce this issue:

1. Create a database in module with the name Database, that inherits from bob.pad.base.PadDatabase
2. Try to compile documentation that includes Database

Error observed (in short Sphinx thinks it is a bob.bio.base.Database instead of a bob.pad.one):

Exception occurred:
  File "/Users/andre/conda/envs/pad-dev/lib/python3.6/site-packages/bob/bio/base/database/database.py", line 125, in __init__
    e) + "\nPlease implement:\n - the model_ids_with_protocol(...) function with at least the "
NotImplementedError: objects() got an unexpected keyword argument 'purposes'
Please implement:
 - the model_ids_with_protocol(...) function with at least the arguments 'groups' and 'protocol'
 - the objects(...) function with at least the arguments 'groups', 'protocol', 'purposes' and 'model_ids'
 - the annotations() function with at least the arguments 'file_id'.
The full traceback has been saved in /var/folders/b3/7l98n3bd7dqc1stjmgxb9mbw0000gn/T/sphinx-err-415lx64m.log, if you want to report the issue to the developers.