Merge pull request #2915 from EricDunsworth/v3.0-broken-link-fixes

Fixed broken Terms and conditions links and added rel="external" to PHP ...
Icons: Add dual icon for external download

Closes gh-2248
Merge pull request #2917 from nschonni/external-download-icon-fix

Icons: Add dual icon for external download
Tabbed interface: improvements for screen readers

 1. Removed `enter` key behaviour for tabs as it was preventing a
    smooth transition to/from forms mode which resulted in an extra
	`enter` key press being required.
 2. Set `aria-live="off"` for the tablist.  This greatly reduces
    the amount of content read by screen readers when the arrow
    keys are used to change tabs or `escape` is used
    to stop the tab cycle.
 3. Set `aria-live="polite"` on the "Play" button.  This causes
    changes to this buttons text to be spoken.
 4. Backported `escape` key to stop tab rotation.

Discussion is in #1081.
Merge pull request #2920 from patheard/tabs-aria-live

Tabbed interface: improvements for screen readers
Multimedia player: Added label and srclang attributes to caption tracks in working examples (fixes #2935).
Merge pull request #2936 from pjackson28/updatemplayerexamples

Multimedia player: Added label and srclang attributes to caption tracks in working examples (fixes #2935)
Multimedia player: Corrected incorrect data-type on English captions and indenting issue in French.
Merge pull request #2938 from pjackson28/mplayerfixes

Multimedia player: Corrected incorrect data-type on English captions and indenting issue in French
Tabbed interface: fix enter key blocking on tabs

1. `e.preventDefault()` has been removed from the tab's keydown event
   handler.  This allows enter key presses to pass through to screen
   readers that don't implement their own enter key behaviour.
2. The play button only has `aria-live="polite"` set when it has
   focus.  This prevents extra speaking of its changed text.
Merge pull request #2931 from patheard/tabs-play

Tabbed interface: fix enter key blocking on tabs
Gitignore file: Added lib folder.
Merge pull request #2954 from EricDunsworth/v3.0-gitignore-lib

Gitignore file: Added lib folder.
Build: Switch to JSHint RC file

- Based off of jQuery recommendation except double quotemark
- The ant task also doesn't support the "globals" property in the JSON
file
Grids SCSS: Disabled link icons in secondary menus.

Fixes #2364
Closes #2953
Linting: Trim trailing space
Linting: cleanup unused variable warnings
Linting: Enforce onevar option
Linting; Remove pe and jQuery globals

Replaced with jquery JSHint option and the "browser" option for the
theme references to window.
"pe" global only kept for the themes and polyfill where they don't use
the "_pe" cached version
Build: Add jshintignore for CLI based linting