Bug 22206: Add routes to suspend/resume holds

Bug 22206: Add routes to suspend/resume holds

This patch introduces:

- POST   /holds/{hold_id}/suspension { "expiration_date": "2019-01-30" }
- DELETE /holds/{hold_id}/suspension

to suspend a hold or resume a suspended hold, respectively.

To test:
- Apply this patches
- Run:
  $ kshell
 k$ prove t/db_dependent/api/v1/holds.t
=> SUCCESS: Tests pass!
- Sign off :-D

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>