Fixes 10505: Document more of LESS vars and mixins

BS3 commits: f1869771bc8b8e8a6c7a98385ec58e0bf0d2d98e
mention lack of support for split button dropdowns in vertical button groups

BS3 commits: fd4130534f6453bbe9c306cfd0869ee6599394b1
Add well-border variable

BS3 commits: 4afcebe0e71aafd0cfb501548a6591effdbe2e70
Document new modal sizes

BS3 commits: d79431ca02683c9d1c754201260f66e5dda15614
Added opacity to customizer and rebuilt customizer

BS3 commits: 3bfa630d2afe70452861b2466daab78daa47dda8
add missing modal variables
Fixes 10921: Add support for input groups within button toolbars

BS3 commits: 544b8ecab78c322bf826797374c0b10279cedf1f
Fixes 10370: Improved and deprecated dropdown menu alignment options

BS3 commits: 11c6ab767cab5384188a301f7c9366b212432e81
rm unused vars

BS3 commits: 35dd6b9fd7a9d06c7bc630abe391bfdf0f4ba644
change class name

BS3 commits: 67b536ea51108c655ac59f1371f11fd8867eaf16
Reduce size of the visibility styles

BS3 commits: 2b56ff04614c4617355d16c14784654e841bcf4d
Fixes 11572: Add contextual background-color classes to match text classes; move both sets of classes to Helper Classes section of the CSS docs

BS3 commits: 072ccd4ddad1dcf642e27497c5253ce578182719
Fixes #11555: Add `@tooltip-opacity` variable

BS3 commits: 647e9eb0f192a18ee84b7e8a4ca162354d98cebb
Fixes 11588: Scope font-size to only p elements in a .jumbotron and remove the supersized line-height from the base class

BS3 commits: 168469f545a189fa51e5d36546e7972f4748ec3f
grunt
Fixes 10921: Add support for input groups within button toolbars. Fixes 10370: Improved and deprecated dropdown menu alignment options. Fixes 11561: Add float: left; to .form-control within input groups to prevent IE9 from screwing up placeholder text and select menu arrows. Fix 11400 and 11431. Reduce size of the visibility styles. Fixes 11572: Add contextual background-color classes to match text classes; move both sets of classes to Helper Classes section of the CSS docs. Fixes 11588: Scope font-size to only p elements in a .jumbotron and remove the supersized line-height from the base class

BS3 commits: 544b8ecab78c322bf826797374c0b10279cedf1f,
11c6ab767cab5384188a301f7c9366b212432e81,
432b9f9cde8e2b067fd54ed148c5f8df510e30c5,
aad447e29075b52a46931be17a9be4016cc89ef1,
2b56ff04614c4617355d16c14784654e841bcf4d,
072ccd4ddad1dcf642e27497c5253ce578182719,
168469f545a189fa51e5d36546e7972f4748ec3f