Switch to separate vars for alert vertical/horizontal padding

Add vertical-align utilities

- Adds six new utils for vertical-align property
- Documents the additional classes in the utils docs

Revert "Drop the $small-font-size variable for the newer $font-size-sm one"

Change SauceLabs iPhone test to use Appium.

Update scrollspy navbar example.

Fixed #20897 by changing btn-default to btn-secondary in docs for V4

v4: Fix outdated utilites classes

Convert Collapse accordion from Panels to Cards

Updated Download docs

[Fix #17611][V4] Change destroy to dispose for tooltip in _JQueryInterface

Strip $ from copied shell commands.

[Fix #17555][V4] fix resetting style on closing collapse

Fix Travis errors due to npm/npm#14042.

Set height on custom select

Matches the changes from #20874 to the regular select element. This is really only necessary for IE and Edge near as I can tell. Fixes #20810.