add `eval` group to utfvp database

In this MR, eval group is added to the utfvp database. Please note that eval group is defined in nom protocol and it was missed in the previous version of bob.bio.vein.

Many thanks to @andre.anjos for all his help!

bob/bio/vein/database/utfvp.py

@@ -46,8 +46,8 @@ class Database(BioDatabase):
         from bob.db.utfvp.query import Database as LowLevelDatabase
         self._db = LowLevelDatabase()
 
-        self.low_level_group_names = ('train', 'dev')
-        self.high_level_group_names = ('world', 'dev')
+        self.low_level_group_names = ('train', 'dev', 'eval')
+        self.high_level_group_names = ('world', 'dev', 'eval')
 
     def groups(self):