toast - Added mac support

[liiight]

Motivation for changes:

Make toast notifications work on MacOS

Detailed changes:

• Requires pync

Config usage if relevant (new plugin or updated schema):

tasks:
  not_test:
    mock:
      - {title: 'bla', url: 'https://flexget.com'}
    accept_all: yes
    disable: seen
    notify:
      entries:
        message: '{{title}}'
        via:
          - toast:
              timeout: 3
              url: '{{ url }}'