New selfservice management module

There is a new selfservice management module placed in the plugins folder:

    plugins/modules/ipaselfservice.py

The selfservice module allows to ensure presence and absence of selfservices
and manage selfservice attributes.

Here is the documentation for the module:

    README-selfservice.md

New example playbooks have been added:

    playbooks/selfservice/selfservice-absent.yml
    playbooks/selfservice/selfservice-present.yml
    playbooks/selfservice/selfservice-member-absent.yml
    playbooks/selfservice/selfservice-member-present.yml

New tests for the module:

    tests/selfservice/test_selfservice.yml