Use python json module instead of simplejson
New feature : Filter layers data by authenticated user group

* For configured layers, the data displayed in the map, popups, print export is filtered. The filter is based on the authenticated user groups, which must match one of the attribute values for the configured layers.
* It is possible to let some users always see all the data by setting the appropriate right in Lizmap admin panel for a group of users
* Some feature with 'all' in the filter attribute will always be accessible by any user.
* Feature kindly sponsored by: Territoires & Paysages, Avignon, France
Prepare release for 1.9.4