[2.3.0] Wrote release announcement
[2.3.0] Compiled blog
[2.3.0] prepare site for release

- update homepage, download links, doc links
[2.3.0] Updated contributors list

- 560!!!
Merge branch 'releases/2.3.0'

2.3.0 readiness
Update default manual version to 2.3
Recompile blog to pick up footer changes in layout

- new default manual version
Merge branch 'hotfix/default-manual-version'
Update images for manual

- Updated images
- Added new images
Merge branch 'hotfix/manual-2.3.0-images'
Replace ZF2 advanced class banner with cert course banner
Merge branch 'hotfix/zf2ca-banner'