- Using the grid classes, they still need clearfixes since rows aren't injected between them all
- Update docs to fix broken classes

This reverts commit deeb74e3.

Reverts #18038
Fixes #18992
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- Rename -height to -height-base to match other vars
- Drop use of -height across the board and rely on it to be inherited
- Adjust padding of .dropdown-header to account for different line-height of h6 heading element (this needs refactoring for variables and rems also)

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/fyi @mdo

Fix #17166

Fix #17052

- new vars for .lead size and weight (previously had none)
- new var for default margin-bottom on h1-h6 elements (previously had none)
- rearranged vars to combine two typography sections into one in variables.scss
- reassigned border-width var to hr-border-width
- made hr-border more specific as hr-border-color

Use grid classes or mixins on .dl-horizontal, update docs to include it, removes auto truncate and makes .text-overflow mixin into a .text-truncate class and mixin combo for better granularity