have modals use auto margin on sides and widen it instead of positioning and negative margin. Input groups overhaul

BS3 commits ce5737870545b908da0dd0744906edd12a9c126c,
b281ad64096d919145159ffbc4e1a5b284708d9b
Input groups overhaul

BS3 commit b281ad64096d919145159ffbc4e1a5b284708d9b
temporarily undo @fat's scrollspy enhancement since it fucks firefox and ie

BS3 commit 4f793752c5d512333a10f55196bbdf4b67662f84
Input groups overhaul. Remove back to top link from docs

BS3 commits b281ad64096d919145159ffbc4e1a5b284708d9b,
7b6f85c1799ea05471d955e2148a3bf9d7b3b541
Input groups overhaul. Safari handles <fieldset disabled> just fine Remove back to top link from docs

BS3 commits b281ad64096d919145159ffbc4e1a5b284708d9b,
89746174b73f36fcb6a85c4a1bf99878e77a6f51,
7b6f85c1799ea05471d955e2148a3bf9d7b3b541
Remove back to top link from docs

BS3 commit 7b6f85c1799ea05471d955e2148a3bf9d7b3b541