Changes for Python 3 (and 2) support

[alexandrenorman]

Hello,
This is an update to make it work with python 3.
Regards,
Alexandre

[sternmotor]

As far as I can see the failed check states a minor problem, fixed by changing 3 locations in users.py. Could this request be merged then?

+++ seafileapi/user.py  2019-03-21 16:29:34.387256042 +0100
@@ -1,4 +1,7 @@
-from group import Group
+try: 
+    import group
+except ImportError:
+    from . import group
 
 
 class Users(object):
@@ -80,11 +83,11 @@
         return resp.json()
 
     def __get_groups__(self):
-        manage_group = Group(self.client)
+        manage_group = group.Group(self.client)
         return manage_group.get_groups()
 
     def __get_id_from_group_name__(self, group_name):
-        manage_group = Group(self.client)
+        manage_group = group.Group(self.client)
         return manage_group.get_id_from_group_name(group_name)