Use the keyword field to add chosen keywords to the metatags

Problem/Motivation

I noticed that using the module generates keywords in the keyword field based on the page content. Seeing as the keyword field is not used by search engines to identify the page topic (nor do people check it), I suggest using the field to manually add keywords and those keywords would be used in the title tag and meta description.

For example: I'm writing a blog on 10 best SEO webinars. I add "best SEO webinars" as the keyword in the keyword field, and it would be added to the title tag and meta description.

Steps to reproduce

1. Create a page or a blog.
2. Fill in content: title and body text.
3. Click Generate Metatag.
4. Go to META TAGS > BASIC TAGS and check the Keyword field (see: sc_keywords.jpg)

Proposed resolution

1. Create a page or a blog.
2. Fill in content: title and body text.
3. Fill in keyword field (see: sc1.jpg).
4. Generating the metatag would add the keyword in the keyword field to the metatags.