Fix up broken input group example layouts
Fixes #8175: Update input min-height vars to fix FF21 input rendering
Remove WebKit overflow scrolling for now
redundant lines removed
upgrade holder to 2.0, update thumbnail examples in docs to fit inside containers
CSS docs page: backticks ==> <code>
Merge pull request #8188 from cvrebert/patch-1

CSS docs page: backticks ==> <code>
Merge pull request #8187 from imsky/3.0.0-wip

upgrade holder to 2.0, update thumbnail examples in docs to fit inside containers
components docs: backticks ==> <code>
Merge pull request #8189 from cvrebert/patch-2

components docs: backticks ==> <code>
Merge pull request #8184 from FLOKER/3.0.0-wip

redundant lines removed
Better base `ul` and `ol` styles

Turns out we were nixing the default browser spacing for bullets and
numbers, so this reverts that and instead just twerks the top/bottom
`margin`.
Remove explicit, unncessary `line-height` on `li` elements
Properly unstyle the `.list-unstyled` class by switching from `margin` to `padding`

Also add better comments
Better clearing on `.dl-horizontal` for empty `dd` elements

Instead of clearing the entire `.dl-horizontal`, we've moved the
clearfix mixin to the `dd` level to solve two problems in one: empty
`dd`s mid-list, and empty `dd` as the last child.

Addresses a few old issues, including #2824, #3819, #3821, #4062,
#6707, and #7180.

Sorry that took so long :D.