Use correct, non-home partial on archive pages' LMP posts.

[benlk]

Changes

• Creates new function largo_load_more_posts_choose_partial(), which returns the slug of the partial that should be combined with partials/content- to get the correct partial to render content with get_template_part( 'partials/content', $partial );
  This function detects the following archive pages and replies with the corresponding partial slug:
  • series with series landing page : series
  • series without series landing page: series
  • category: archive
  • author: archive
  • tag: archive
  • date: archive
  • argo links posts: argolinks
  • unspecified: home
• largo_load_more_posts() now uses largo_load_more_posts_choose_partial()

Why:

For #868, where the category archive page was using partials/content-archive.php but the LMP on that page was returning partials/content-home.php.

On the decision of slug to use: per this comment's research, here are the decisions and rationales:

• series: series, because that's what Largo does
• category: archive, because Largo uses archive for posts in the row. lensnola is based on largo, not largo-dev
• author, tag, date: archive, because Largo uses archive in archive.php for all these types.
• argolinks: argolinks was behavior before this PR
• unspecified: home was behavior before this PR

Questions:

• Should the default be '' and home be a case that is explicitly detected?
• Should the output of this function be filterable?

[benlk]

(Time for this is tracked on WE-15)

[rnagle]

Added a couple things to this:

• The largo_load_more_posts_choose_partial function now takes one argument: $post_query -- the query we're using to build markup for LMP. Doing this rather than decode the $_POST['query'] variable a second time.
• The return value for largo_load_more_posts_choose_partial is now fitlerable using the largo_lmp_template_partial filter. The $partial and $post_query are passed to this filter.

@benlk regarding your questions --

1. I think it's fine to use $partial = 'home' to start. At this time, this will fallback to content.php since Largo does not include a content-home.php.
2. See above.

[benlk]

• merge latest develop
• remove this check: https://github.com/INN/Largo/blob/868-correct-partial-on-archives/inc/ajax-functions.php#L82-L86
• add note to PR and to release notes that if you're going to override largo_load_more_posts_data you will need to make sure that is_home is set correctly: https://github.com/INN/Largo/blob/868-correct-partial-on-archives/inc/ajax-functions.php#L47