Refactor tab navigation helpers
Fix schema.rb after rebase with master
Keep urls hackable

There is little point having an additional "about" page for worldwide
organisations - the show page is all the about anyone will ever need.
To keep the urls hackable, we redirect /about to the show page.
Add flash messages to contacts and social media
Make the block on tab_navigation_for optional

Enclosing the content in a "tab-content" div is only necessary if the
page is using js-powered "tabbable" tabs. This makes passing a block
to this helper optional to keep things simpler when js tabs are not
required.