Review follow up

- Tweak whitespace in avocetfloatingnavigation.html
- avocetfloatingnavigation.css:
  - Add license header
  - Scope all styles to .avocetfloatingnavigation-wrapper
  - Order properties (where appropriate)
  - Add newline at end of file
- avocetfloatingnavigation.js:
  - Move rendering into a function
  - Fix some comments
  - Use new widgetsready event to detect page load