Seek-and-destroy flex box incompatibilities
Give value entries a fixed width to avoid them shifting left
Box tabs now extend to use full width of page
Use raw createElement rather than use jQuery's tag parsing mechanism
Require Ruby 2
Replace UIDs with the idea of 'singleton' pages

This removes the last bit of developer-only content from the database.

Instead of relying on db-held UID values to retrieve single pages in a reliable way, developers now define singleton types in code and are able to reference their instances using a set of given 'labels'.

Once declared as a singleton editors (including developers) are prevented from creating more than one instance of that type.
Fix content hash calculation for aliases

Previously aliases pointing to different targets but with the same field values would return identical content hashes
Move to new hash style
Remove Context#site_page - singleton classes replace it's most common use case and I never liked it anyway
Stop constant closing & re-opening of events connection