Resolve "file-list database is not tested anymore"

Closes #52 (closed)

I have implemented a FileListBioDatabase on the basis of the old DatabaseFileList. There is one main difference: The bob.db.bio_filelist database is now instantiated inside FileListBioDatabase and does not need to be passed to the constructor, as it was the case in DatabaseFileList.

I have re-added the test case that makes sure that this database is actually working as expected. I haven't spent too much time for documenting the database interface, except for the constructor (this is the only contact point that a user should have with this database, anyways). I have added a new dependency for this package, which is bob.db.bio_filelist. I think this should not create any problems.

Note that the documentation will only work after bob.db.bio_filelist!4 (merged) was accepted.