Reinstated CDN links

- Re-added CDN links, pointing to new location.
Merge branch 'hotfix/cdn-links'
Removed all references to phpcloud

- Being sunsetted as of 7 September 2014; no new registrations as of 6 August
  2014.
Merge branch 'feature/remove-phpcloud-refs'

Removed all phpcloud references, due to sunsetting of that service.
Training pages/content update

- Added icons for each ZF2 training offering to main "learn" page, and
  moved webinars to end of content of that page
- Updated training/certification page to add icons for each offering,
  and to add entries for ZF2 advanced training and certification
  offerings.
Added rotating ads for training/certification

- Homepage
- Downloads sidebar
- Learn section sidebar
Merge branch 'feature/training-content'

Updated training content and ads