Add module priority setter CLI command

Module priority CLI command
###########################

Priority in CK modules is used to set the execution order of all enabled modules.
Currently, the priority value can only be set with the REST API.

This blueprint proposes to add a CLI command to set the priority of a module

Work items:

- in V1/shell.py, update *do_module_list* fucntion to also print the *priority* field
- in V1/core.py, add a method *set_priority(self, priority)* to *CloudkittyModule*
- in V1/shell.py, add a do_module_set_priority to create a new CLI command