Add title type toggle for breadcrumbs

[sybrew]

I'm extracting a new issue from #668 (comment) so that we can work on it for the minor release cycle.

This is the most pressing and requested feature for the breadcrumbs: Add a toggle to select the title type. This should affect both the Schema.org breadcrumbs and shortcode output.

[We] should probably replace the Meta\Title::get_bare_title() calls with a new get_breadcrumb_title() call, where we can easily switch over settings. We shouldn't care too much about the structured data; instead, we should let that mimic what the user sees on the front end.

New sites should have "Page title."
Old sites should have "Meta title."