Support: clean up comments and Support notation

Closes gh-1577
CSS: Do not throw on frame elements in FF

IE9-10 throws on elements created in popups (see #14150), FF meanwhile throws
on frame elements through "defaultView.getComputedStyle" (see #15098)

Use "defaultView" if in the popup which would fix IE issue,
use "window.getComputedStyle" which would fix FF issue.

And everybody wins, except performance, but who cares right?

Fixes #15098
Closes gh-1583
Ajax: Always use script injection in globalEval

Fixes #14757
Closes gh-1449
Effects: Reintroduce use of requestAnimationFrame

Same as before, just use don't use prefixes, since they pretty match useless now
and use page visibility API to determine if animation should start.

Also null the requestAnimationFrame attribute in window for tests since
sinon does not provide fake method for it.

Fixes #15147
Effects: Improve raf logic

* Make animation behave as if jQuery.fx.off = true if document is hidden

* Use cancelAnimationFrame in jQuery.fx.stop

Closes gh-1578
Build: Move test to appropriate module
Build: Update commitplease dev dependency
Build: Upgrade to grunt-bowercopy 1.0.0
Build: Remove unused Sizzle test files
Build: Move all external libraries to external directory

Closes gh-1593
Build: ignore test dependencies for npm install
Build: update Sizzle to 1.11.1 and include license
Build: update grunt-bowercopy