Add schema BreadcrumbList

[EkoJR]

Resolves #2813

Proposed changes

Adds breadcrumbs to the schema structured data.

Types of changes

What types of changes does your code introduce?

• New feature (non-breaking change which adds functionality)
• Improves existing functionality

Checklist

• [x] I've selected the appropriate branch (ie x.y rather than master).
• [x] I've created an appropriate title, descriptive of what the PR does.
• [ ] Travis-ci runs with no errors.
• [ ] I have added tests that prove my fix is effective/my feature works or have created an issue for it (if appropriate).
• [ ] I have added necessary documentation, or have created an issue for docs (if appropriate).

Testing instructions

1. Navigate frontend and check ld+/json data in a. Home/Main b. Post c. Child Page d. Taxonomy Term archive. e. Date archive. f. Author page. g. Search page.

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[benjaminprojas]

@EkoJR is there supposed to be a BreadcrumbList on the home page? I'm not seeing one there at all, which is okay if its not meant to show. I just see this:

...
"breadcrumb": {
    "@id": "https://aioseo.local#breadcrumblist"
},
...

[EkoJR]

@wpsmort @benjaminprojas The error should now be fixed on the Homepage.

[EkoJR]

@benjaminprojas Added a fix for handling $wp_query->is_posts_page instance/condition.

[wpsmort]

This is tested and is good.