Don't run post build during PR testing

Check Travis's env variable TRAVIS_PULL_REQUEST to see if the post build
should be run at all
Migrated repetitive footnote highlighting properties into SCSS placeholder selector.
Set default footnote link background colour to white when situated in parent containers that leverage the "background-light" class. Fixes issue #916.
Merge pull request #929 from EricDunsworth/v3.0-footnotes

Minor Footnotes fixes/enhancements
Fixed #914 - Prevented the overlay to trigger a form post
Merge pull request #934 from LaurentGoderre/v3.0

Fixed #914 - Prevented the overlay to trigger a form post
Optimized body div references and improved support for wb-body-sec-sup.
Use public Travis build number in commit message

I previously set the job ID instead of the build number as described in
the documents
http://about.travis-ci.org/docs/user/ci-environment/#Environment-variables
Use extends rather than regular expressions

More selectors, but better performance
Use @each expansion for downloadable file types

Adds readablity and maintainablity
Space not required after mailto:
background-position: 0 0 is the default value

This is not the case with multiple backgrounds, but that does not apply
to icons
Extend download iterator

Previous version output single classes for each member of the array
Use iterators for sprites

Note to change the sprites to a single column at a later date
Added summary element support to Grid SCSS button classes.
Fixed display of breadcrumb images in GC Web Usability theme.
Added fallback background colour for GC Web Usability intranet banner (to avoid white text on a white background).
Use sequential gem install

For issue with Travis
Merge pull request #946 from nschonni/sequential-gem-install-940

Use sequential gem install
Merge branch 'travis-skip-pull-requests' of github.com:nschonni/wet-boew into v3.0