Implement an offset anchor dynamic CSS class.

`.wdn-offset-anchor` is generated at runtime to use the calculated
navigation bar size.

Closes #667
Update list of WDN colors
Header color updates
Resources color updates (login icon)
Darkened login icon a bit more
Navigation color updates
Header top bar color update
Update cupola image to match footer background color
Share menu color updates
Color updates for forms
Search style updates
Removed unnecessary commented-out style
Bumped dependency version number to 4.0.14
Merge pull request #760 from skoolbus39/wdn-color-list

Update list of WDN colors
Removed placeholder text and wdn-input-group, adjusted icon colors
wdn-input-group removal mistakenly not included in last commit
Added colors for (visually hidden) labels to pass accessibility tests
Update brand color in 'N' flag images
Updated image didn't match size of original
Add margin to form list elements and remove from wdn-button.