Merge pull request #419 from ambiata/topic/undata

A smaller version than the original remove ivory-data PR.
A moderate attempt to remove unsafe/unused code.

This is far from what I would call acceptable, but it is a step
towards containing the differences of repository types again.
It is going to be difficult until s3 is end to end, but we
need to do better at making sure all platforms are supported
on non-mr code for now.
Merge pull request #417 from ambiata/topic/remove-unsafe

A moderate attempt to remove unsafe/unused code.
Removed no-incremental from snapshot.

It was not being followed uniformily, it was causing test code
to follow non-production paths, and was just more useless code.
Added commish to release notes.
Merge pull request #418 from ambiata/topic/no-incremental

Removed no-incremental from snapshot.
Rename Snapshot -> Snapshots.

Main reason is to free up noun to allow core data types to be consistently
named. This is the first step in my plan changes, PR'ing so that
it can be cherry picked by others if required given it is a bit
of a pevasive little thing.
Merge pull request #423 from ambiata/topic/snapshot-rename

Rename Snapshot -> Snapshots.
Some renames for consistency and to make sense.
Merge pull request #421 from ambiata/topic/renames

Some renames for consistency and to make sense.
Removing unused code.

Most of this was just taking up space, and makes
my change a lot harder, so yeh, goodbye.
Merge pull request #425 from ambiata/topic/bring-out-yer-dead

Removing unused code.
Issue #301 - Validate consistency of count_by
Merge pull request #426 from ambiata/topic/reduction-properties

Validate consistency of count_by
Merge identifier variants whilst keeping compatibility.

This will smoothly migrate all identifiers to V2.

Fixes #56.
Fixes #79.
Fixes #149.