Vertically align content

Vertically align content in columns on home page
Links open in new page
Merge pull request #407 from Coenego/issue-397-links-in-new-tab

Links open in new page
Follow-up on review

Images are centred horizontally again.
Merge pull request #405 from Coenego/issue-399-vertically-align

Vertically align content
Fix avocet.skin.css code style issue caught by qunit test
Merge pull request #409 from bp323/fixQunitTest

Fix avocet.skin.css code style issue caught by qunit test
Merge branch 'master' into issue-255-back-button