Use styled HTML for documentation widgets

[#55151702]
Switch to using javascript widgets using site styling

- Quickstart selector is implemented using bootstrap-select rather than the dropdown button used elsewhere
- Quickstart selector is still to be styled
Added bootstrap select for quick start

[#52044647]
Merge branch 'gh-pages' of https://github.com/spring-projects/gh-pages into gh-pages

* 'gh-pages' of https://github.com/spring-projects/gh-pages:
  Added bootstrap select for quick start
  Switch to using javascript widgets using site styling
  Use styled HTML for documentation widgets