Bug 37943: Log object create as JSON diff, implement for items

Bug 37943: Log object create as JSON diff, implement for items

We should store newly created objects as diffs just as we do for modifications.
This enhancement will store modification diffs if the action is set to ADD or CREATE and an "original" object is passed in.

Test Plan:
1) Enable CataloguingLog
2) Create an item
3) Query the database for the newest action log:
   select * from action_logs order by action_id desc limit 1\G
4) Note the diff column is NULL
5) Apply this patch
6) Restart all the things!
7) Create another item
8) Query the database again
9) Note the diff has been created!

Signed-off-by: Sukhmandeep Benipal <sukhmandeep.benipal@inLibro.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>