add basic back to top link to docs sidenavs, fixes 12589

BS3 commits: f16a2376c11ac8946c4aee102ff141117815e2de
Allow the bootstrap package in npm to expose css and less

BS3 commits: 81d9a46dcd756484ece9ad0fae1de09b8fdabff5
Docs: losslessly compress images.

BS3 commits: 7eb532262fbd1112215b5a547b9285794b5360ab