Update effective-forms.md

Replaced with a ton of content from "Designing transaction" in the Gov.uk Service Manual (https://www.gov.uk/service-manual/user-centred-design/designing-transactions.html), which uses the Open Government License v2.0 (http://www.nationalarchives.gov.uk/doc/open-government-licence/version/2/.
Update effective-forms.md

fixed image links
Update effective-forms.md

Updated more links
Update effective-forms.md

Added information about communicating errors
Merge pull request #157 from ohsk/gh-pages

Update UI Toolkit > Grids and Layout page
Update effective-forms.md

content edits about validation and helping users
Update effective-forms.md

Updated Table of Contents
Update effective-forms.md

adjusted attribution language
Update effective-forms.md

copy edits for line 24. not loving it yet.
Update guides.md

updated overview text to match the other two sections a lil better
Merge pull request #158 from benguhin/patch-1

Update guides.md
Update identity.md

removed the third sentence
Merge pull request #159 from benguhin/patch-2

Update identity.md
Update ui-toolkit.md

added designer credit :) and tried to make the last part more active
Update buttons.md

Removed sentence about destructive actions in the header - it's better explained in the dedicated section later in the page
Update expandables.md

Updated intro to make it more consistent with buttons and links
Update links.md

Removed "should"
Update pagination.md

- simplified the mentions of infinite scroll
- updated the usage to be more about how to use the component
Make color page responsive; remove date from banner
Update buttons.md

Removed note about destructive actions in the header. It's not important enough to be that far up.