Add plugin to pretty print Ansible msg output

[fullyint]

This PR proposes a new 'stdout_callback' named output.py to augment Ansible's default.py. It extracts and displays the msg attribute, interpreting newline characters and applying textwrap.

This PR adds a couple .py files, still mirroring Ansible project's structure.

lib/
  trellis/
    modules/
      deploy_helper.py
    plugins/
      callback/         <-- new
        output.py       <-- new
      filter/
        filters.py
    utils/              <-- new
      output.py         <-- new

Run the playbook below on Trellis master then again on this PR's branch to see the different formatting.

- name: Output demo 
  gather_facts: false
  hosts: localhost
  vars_files:
    - group_vars/staging/wordpress_sites.yml
  tasks:
    - debug:
        msg: If `with_dict`, `item` below displays dict key only (unless `-v`)
      register: results
      with_dict: "{{ wordpress_sites }}"

    - debug:
        msg: If `with_items` based on dict, attempts to display only key (unless `-v`)
      with_items: "{{ results.results }}"

    - assert:
        that: "{{ item.name == 'bar' }}"
        msg: |
          {{ item.msg }}

          {{ item.msg }}

          {{ item.msg*2 }}
      with_items:
        - {'name': 'foo', 'msg': 'Fail for item zero.  '}
        - {'name': 'bar', 'msg': 'Example ok/skipped item'}
        - {'name': 'foo', 'msg': 'The horizontal rule between hosts/items helps distinguish between multiple hosts/items, especially when messages have blank lines. Blank lines would no longer clearly mark the start/end of the message per host/item.  '}

This is an improved piece of #531.

[swalkinshaw]

So much better 👍