Make text analysis functionality modular

[timbocode]

As per https://forums.classicpress.net/t/classic-seo-beta-1-released/2115/2.

If test analysis is disabled, this removes the only place the only place to edit post meta titles and descriptions.

See also https://petitions.classicpress.net/posts/175/allow-editing-of-page-title-and-meta-description-seo.

But making the functionality modular is worth considering for those that don't need it.