Various typos, grammar fixes, title casing and sentence forms

- "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
Seed language files with SEO definitions

Warning about turning on dofollow setting in SEO Feedback
should be more cautionary in tone than casual.
Merge pull request #118 from randomecho/copyedits

Missing SEO blocks in language definitions and minor grammar fixes