FormSave per lutostag

Automatically saves any textarea typed in, and allows the user to view saved textarea content by clicking on a button.

As an example if you go to: http://www.yamllint.com/ and type in that box it will be saved automatically, when you click on the FormSave icon you can view the content for any previously saved sites.

If there is a particular website that this addon does not work on (besides addons.vaultpit.io, which is disabled for security -- see here), please mention the page with a full link to a page that does not work either in a bug against the project at github or in your review below.