Etsy OpenSearch Engine wót aminomancer

Adds a search engine for etsy.com that you can use from the search or address bar. Also includes an SVG icon with context properties, so it can be made to look good with both light and dark themes, rather than always being bright cyan (requires userChrome.css).

Search provider details:
name: Etsy
search_url: https://www.etsy.com/search
search_form: https://www.etsy.com/search?ref=tab_search&q={searchTerms}
search_url_get_params: ref=tab_search&q={searchTerms}