Added field for meta keywords.

[john-mad-biker]

In our company we're needed to set meta keywords for every page of content. Now seo-metadata editor have 1 more field - keywords =)

And also styles for text inputs and textareas becomes more unified (style for '2-col' area, where is located 'title' and 'description' fields, and for '1-col' area, where 'URL Name' field placed).