Merge branch 'filebase-api-fix' into 'master'

Added the protocol argument issue #111

Closes #111

See merge request !153

bob/bio/base/database/database.py

@@ -294,7 +294,7 @@ class BioDatabase(six.with_metaclass(abc.ABCMeta, bob.db.base.FileDatabase)):
         raise NotImplementedError("Please implement this function in derived classes")
 
 
-    def groups(self):
+    def groups(self, protocol=None):
         """
         Returns the names of all registered groups in the database