Post Edit List Columns

[scottnelle]

This PR makes the following changes:

• Adds a new Post List UI column "Authors" to any post types which support Byline Manager, listing the byline Profiles for each post and linking each profile name to a list of that profile's posts.
  ** Adds a filter to disable this new behavior, in case your project already has an implementation that you already like. You can use add_filter( 'byline_manager_modify_post_edit_columns', '__return_false' ); to bypass the new behavior.
• If the authors column is present, that column is re-labeled "Created By" to distinguish that it is the WordPress user who entered the content in the CMS, not necessarily the Author(s) of the post.
  ** By default Byline Manager disables author support altogether for any post type which supports Byline Manager, but that behavior is filterable and so it is worth supporting this override behavior.
• Increments the plugin version and updates the Tested version of WordPress in the root plugin file.

Note that if your project already includes a custom implementation to

Big props to @dlh01 on this one. It borrows heavily from his work across many projects over the years.