Add TidyAll test.

This will break builds for people who don't have the pre-commit hook
installed, which is a _good_ thing.
Tidy everything.
Add Image element to OpenSearch document
Merge pull request #1167 from oiami/Add_favicon_url_to_opensearch_xml

Add Image element to OpenSearch document
Use a separate 16x16 ico for opensearch

Opensearch limits icon size to 10,000
(and the ico with multiple sizes is too large).