Add log type

[gsf]

Add log type with the following fields:

• timestamp
• user
• action (created, updated, deleted)
• itemId
• diff

Log entries will be added with each item set and delete.

[gsf]

Consider using https://github.com/flitbit/diff for object diffing.

[gsf]

The diff should have "index": "no" in the mapping.

[gsf]

Diff should be from "after" to "before" to enable some kind of rollback. Otherwise, we should just save the "before" with each log entry. Either way, we're looking at a potential explosion in index size.

[gsf]

Also if we're diffing we need to consider updates to all related items as well.

[gsf]

Okay no diffs in the log entries, just the "before" snapshot of the item before the action is taken.