Use the Bundle builder for serialization.

This looks a bit neater and involves slightly less copying when
metadata is serialized. Also serialize '_' properties when not
in lite mode.
Serialize, by default, the first subject of a system event.

Also ensure that the number of subjects is cached in _childCount
property.
Add a script to add missing childCount on system events
Enable item counting for Country/Repository. TODO: Remove code dup.
Quick hack to prevent metadata being zapped on item update. TODO: permenant fix
More changes to (still dubious) rel caching scheme, inc. housekeeping REST func to rebuild caches.
Allow filtering the event stream by some specific useful criteria
Add 'base' EAD Handler that has default empty methods for extraction or update of title, id, language and dates and make BA EAD Handler subclass of it.
Use a static FramedGraphFactory, which prevents a PermGen leak
Add NIOD EAD test (does not pass yet, because relations are not created as Maps). Update BA handler.
Add logger to NIOD test, ignore access points while Importer expects pretty different objects for them, add '1999/2000' as accepted date (range) format
Add special commands for NIOD and BundesArchiv EAD importers.
Remove logback settings from git
WIP user follows work
Add a way to follow/unfollow users
Add a way of checking if one user follows another
Expand social-networky stuff
Add API for users to watch items. Make following API more flexible
by not assuming all calls pertain to the user making the call.
Add watchable interface and implement watching items
Add an experimental 'personalised' event feed.