New attempt at fixing sort on meta field

[perifer]

This does the sort as described in https://www.advancedcustomfields.com/resources/orde-posts-by-custom-fields/

$query->set('orderby', 'meta_value');	
$query->set('meta_key', 'start_date');	 

I don't know what $metaQuery did before. It is remove in this commit.

I also change the logic around _meta_key_ check. This now checks that it is a prefix, not just part of the string. I think that is more correct.

[perifer]

Let me know if I can do anything to get this in a tagged release.

[perifer]

Let me know if I can do anything to get this in a tagged release. The functionality should be identical to the one that was merged into Municipio some time ago.

[sebastianthulin]

Conclusion: Will cause issues with NULL meta (posts will not show).