Ansible Restructuring

This PR changes the high-level ansible structure from

  roles:
      - { role: common, tags: ['common'] }
      - { role: network, tags: ['network'] }
      - { role: gateway, tags: ['gateway'] }
      - { role: core, tags: ['core'] }
      - { role: xsce-addons, tags: ['addons'] }

to

  roles:
      - { role: 1-prep, tags: ['prep','platform','base'] }
      - { role: 2-common, tags: ['common','base'] }
      - { role: 3-base-server, tags: ['base'] }
      - { role: 4-server-options, tags: ['options'] }
      - { role: 5-xo-services, tags: ['xo-services'] }
      - { role: 6-generic-apps, tags: ['generic-apps'] }
      - { role: 7-edu-apps, tags: ['edu-apps'] }    
      - { role: 8-mgmt-tools, tags: ['tools'] }
      - { role: 9-local-addons, tags: ['addons'] }     

A Readme.rst has been added to each to describe what should go there.

Testing:

This PR installed successfully on both an XO4 and an x64 VBox VM
All tests in https://github.com/XSCE/xsce/blob/master/docs/TESTING.rst were conducted.
The only exception was that backup did not happen, but this was true for release-5.0
as well.