Add whitespace in front of offline contacts

In the roster view, online contacts are prefixed with '[+] ' to show their presence, which adds four characters of indentation. Offline contacts are not indented, so if the roster is sorted by name only, there is a mixed indentation in the list. Besides of violating python coding guidelines, this makes looking for a certain contact much harder.

Please make all roster entries vertically aligned by inserting ' ' in front of offline contacts.

• Changesets:
  • Revision 76a890ac by mathieui on 2016-06-24T17:34:23Z:

Fix #3203 (indent contact and resources in the roster)