Apply @color argument to striped gradient

The @color argument is currently not being used for the striped gradient.
Remove progress bar striped @color parameters; use default transparent white.

* If the @color parameter is not removed, the stripes are the same color as the element background color. In this case, the stripes do not appear.
Fixing carousel control positioning

The left control should be positioned from the left, while the right
control should be positioning from the right. Positioning both from the
left results in the right carousel control being incorrectly positioned
(most noticeable with a larger than normal font size).
Add missing methods (rotateX/Y, perspective(-origin) and transform-origin)

Added missing mixins:
rotateX
rotateY
perspective
perspective-origin
transform-origin
Make custom max-width on row conform to Boostrap convention

Bootstrap break point for tablet portrait 768 keeps the row intact, so it's not appropriate to have off-canvas elements at that width. Custom off-canvas.css should be breakpoint 767px
Prevent X-scroll on small screens

html overflow-x must be hidden to prevent accidental x-scroll on small screens. This is more apparent with touch screens, where the user often gestures diagonally instead of a true vertical gesture.
Getting started docs - Migrating section: refactor some of the text for clarity and easy reading.Also removed some rogue tab characters in the source that I introduced in prior commits.
For consistency with the rest of the docs, removed manually line-wrapped HTML text.
No manual line breaks in HTML text as per custom.
Fixes #10436: use screen-sm var instead of hardcoded pixel value
Merge branch 'master' of github.com:twbs/bootstrap
Fixed to lowercase 'v' in 'v3.0'
Removed a trailing space at end of line.
Yet another  manually wrapped text line consolidated
fixed a </p> tag that was on its own line.
Merge pull request #10421 from StevenBlack/GSEdits6

Getting started docs - Migrating section: refactor the text for ...
Fixes #10417: Document `.hidden` in the Helper classes *Screen reader content* section
Merge pull request #10227 from UTCWebDev/master

Fixes 10212 - Make custom max-width on row conform to Bootstrap convention
Merge branch 'master' of github.com:twbs/bootstrap
polish off #10227 with an inline comment