Python: change requirements for protobuff to 2.4.1

the 2.5.0 is not supported by our servers
Merge pull request #595 from antoine-de/requirement_proto

Python: change requirements for protobuff to 2.4.1
navitia : new api pt_objects added

objects network, mode, line, route added
dinctionary autocomplete used
navitia : pt_objects sorted

tests added.
lines commented deleted.
navitia : stop_area added in api pt_objects

Test added
autocomplete : dictionary modified

Networkname, modename and linecode added in line
and route name.
autocomplete : comments modified
navitia : comments modified
protobuf : elements added in places
autocomplete : protobuf pt_object used for places
autocomplete : function autocoplete used for api pt_objects

Tests modified
autocomplete : corrections on comments