Forms: Add input-placeholder mixin

Backported from Compass vNext (0.13), but modified for the 0.12
definition of legacy Firefox.

Fixes gh-2855
Merge pull request #2865 from nschonni/add-placeholder-mixin

Forms: Add input-placeholder mixin
Merge branch 'v3.0'
GC Web Usability Intranet theme: Added missing image (fixes #2859).
Merge pull request #2869 from pjackson28/missingintranetimage

GC Web Usability Intranet theme: Added missing image (fixes #2859).
Merge branch 'v3.0'
Now hiding .datepicker-format elements when the datepicker polyfill is not loaded.
Merge pull request #2872 from pjackson28/datepicker-format-hide

Now hiding .datepicker-format elements when the datepicker polyfill is not loaded.
Resolved merge conflicts.
Datepicker polyfill: Fixed typo in extends to correct issue in #1170.
Merge pull request #2878 from pjackson28/fixdatepickerextends

Datepicker polyfill: Fixed typo in extends to correct issue in #1170.
Resolved merge conflicts
Datepicker/Form validation: Updated date modified on working examples pages.
Merge pull request #2879 from pjackson28/v3.0

Datepicker/Form validation: Updated date modified on working examples pages
Resolved merge conflicts.
Fixed broken links to forces.gc.ca.
Merge pull request #2882 from EricDunsworth/v3.0-broken-link-fixes

Fixed broken links to forces.gc.ca.
i18n: Add single quote escapes

Additional EditorConfig settings so relevant whitespace isn't stripped
from CSVs
Expand/collapse all: fix native support for details

Browsers with native support for the details element now only have
the 'open' property set (fixes #2881).
Merge pull request #2884 from patheard/expand-collapse-all

Expand/collapse all: fix native support for details