Add mixin for transform: scale(x, y);

The Performance Platform uses this so it's probably useful for others too.
Add browser support documentation to CSS 3 mixins

Data comes from http://caniuse.com/.

I've gone a bit over the top in adding documentation for this. I'm not sure
if this is too far, but I think it's useful. I'm trying to avoid being
prescriptive, but we should be trying to drop old prefixes and not leave
them hanging around forever.

This commit changes the order of the prefixes for gradient() to make them
line up neatly, but should cause no user facing changes.

It also removes the Microsoft prefix on the transition property, because
that has never been a thing.
Add unprefixed linear-gradient() value

Browsers now use the unprefixed version, so we should be trying to
catch problems with it by actually including it.
Add Microsoft prefix for transform: translate();
Make text colour for the phase banner black

Our $black variable (used by $text-colour) does
not provide the correct contrast ratio.
Merge pull request #105 from alphagov/update-phase-black

Improve contrast ratio of text colour for the phase banner
Fix typo in Media player section

Change 'videoss' to 'videos' in Media player section
Merge pull request #108 from pwolstenholme/patch-1

Fix typo in Media player section
Standard GOV UK icons added to toolkit

Previously icons were held in a seperate static repository which would need to be hosted in addition to the frontend toolkit. Putting the icons into this toolkit helps to get all of the resources into one place. It also makes it easier for some developers to pick up any changes to the icons using the NPM/GEM versions.
Merge pull request #109 from thatguynamedandy/add-static-icons

Standard GOV UK icons added to toolkit
Adding three quarters variable to measurements
Merge pull request #110 from alphagov/add-three-quarters

Adding three quarters variable to measurements
Merge pull request #106 from alphagov/improve-css3-mixins

Improve CSS3 mixins