1) The item_updated event no longer takes the old and new items.
Instead we overload ORM to track the original data and make
that available via the item. This will allow us to move event
publishing down into the API methods which in turn will give us
more stability since we won't require each controller to remember
to do it.
2) ORM class now tracks the original values. It doesn't track
the original relationships (no need for that, yet)
3) Added new events:
item_deleted
group_deleted
user_deleted
Significantly speed up the process by copying Gallery2 thumbnails and
resizes wherever possible instead of regenerating them. This requires
us to figure out the dimensions of the original G2 derivative and make
sure that it matches in some reasonable way.
To allow users to take advantage of this, calculate the optimal thumb
and resize size to set in G3 to match what was used in G2. While
we're at it, give the user some idea of how much data is available in
G2 to import.
