Refresh screengrabs and extension metadata

[matatk]

It is possible to use some HTML for the description on AMO at least.

• AMO: Can use some HTML.
• Chrome: Nowhere does it say one can use HTML; consensus appears to be that one cannot.
• Opera: The extension upload site says HTML and BBCode are not allowed.

Therefore, if I am to use HTML, will need to make a script to convert the HTML for Firefox back into plain text for t'others.

[matatk]

Need to include details on why the permissions are needed.