Move from simplejson to standard library json - SL #3816

We should only use one json implementatin, see
http://bugs.sugarlabs.org/ticket/3142

Signed-off-by: Manuel Quiñones <manuq@laptop.org>
Merge pull request #23 from manuq/3816

Move from simplejson to standard library json - SL #3816
Reviewed by Walter (and tested on the latest sugar bits)