Missing SEO blocks in language definitions and minor grammar fixes

- "Add another attachment" should just be sentence cased
- Removed extra full stop on dashboard welcome page
- Typo, name of blogware, needs capital T as a proper noun
- Same for Amazon.com, but also include the .com part
- Match the button names on Sidebar design instructions
- Added language files with SEO definitions

Changed the warning about turning on dofollow setting in SEO Feedback to one that is more cautionary than casual in tone.