add support for user groups

[landam]

Currently GIS.lab users are by default members of gislabusers and gislabadmins (only superusers) group. It would be useful to manage also other admin-defined groups. That would require to add new admin commands like:

• gislab-addgroup
• gislab-delgroup

And a new parameter for gislab-adduser to define membership for newly created users (eg. -r):

-r List of admin-defined groups

sudo gislab-addgroup group1
sudo gislab-adduser -g User -l GIS.lab -m lab1@gis.lab -p lab -r group1 lab1

Then the user lab1 will be member of gislabusers and group1.

Or to modify usage of already used -s parameter (which defines superusers)

sudo gislab-adduser -g User -l GIS.lab -m lab1@gis.lab -p lab -s gislabadmins lab1

sudo gislab-addgroup group1
sudo gislab-adduser -g User -l GIS.lab -m lab1@gis.lab -p lab -s gislabadmins,group1 lab2

Then lab1 will be member of gislabusers and gislabadmins, lab2 --- gislabusers, gislabadmins and group1.

[landam]

It would be also useful to introduce also new admin commands:

• gislab-listusers
• gislab-listgroups

[imincik]

@mpastor , please add tests for gislab-addgroup, gislab-delgroup, gislab-listusers, gislab-listgroups

[imincik]

Implemented in multiple recent commits.