Add self-referential hreflang for multi-locale sites

[architchandra]

It seems that every webpage that has multi-locale versions should have self-referential hreflangs along with hreflangs to the other versions.

As per the link from the SEOMate docs itself:

Each variation of the page should include a set of elements in the element, one link for each page variant including itself.

It would be great if this can be added soon. Thanks!