CSS Updates: responsive and other things

#### What's this PR do?

Adds detail around responsive approach, as well as updating some outdated LESS references, adding some details about file organization, and adding a list of CSS tools in use.

#### Where should the reviewer start?

In `CSS_Standards.mkd`

#### Any background context you want to provide?

We've never had an official responsive approach, now we do.

#### What are the relevant tickets?

https://sprint.ly/product/1/item/8568

#### What gif best describes this PR or how it makes you feel?

![giphy-3](https://cloud.githubusercontent.com/assets/126919/5255783/53ab5bd6-7974-11e4-847f-63adc015b1a5.gif)