feat: Add authoring feature for Community Stories

[jhung]

• I've read the guidelines for Contributing to the Platform Co-op Toolkit
• This isn't a duplicate of an existing pull request

Description

Adds a pcc-story post type to the Admin interface and allows the authoring of content to be featured the Community Voices > Stories section of the front-end site.

To Test

1. Activate the pcc-framework plugin with the changes from this pull request.
2. Go to "Stories > Organization", "Stories > Region", "Stories > Sector" and add a new term to each of those taxonomies.
3. Go to "Stories > Add new"
4. Enter a title and a quote in the body.
5. In the sidebar, specify a Youtube video url (ex. https://www.youtube.com/watch?v=savByUiUvbY&feature=youtu.be)
6. Add a Featured Image
7. Choose a Storyteller (it should be populated with names from the Persons post type)
8. Choose a Sector, Region, and Organization (the terms you specified in step 2 should appear in these lists).
9. Publish.

Expected behaviour

The Story content should save and be listed under "All stories".

Known issues

Currently there is no input validation. See #162 .

[jhung]

There are some changes from other commits in the history. These changes need to be verified.

Also package-lock.json was modified and probably shouldn't. I can revert it, but awaiting feedback first.

[greatislander]

This works great for me. The one change I'd recommend is adding a link below the Storyteller dropdown to add a new storyteller(/wp-admin/post-new.php?post_type=pcc-person) in case there isn't a "Person" for the storyteller.