Bug 15486: Extend CanItemBeReserved so it handles daily holds limits

Bug 15486: Extend CanItemBeReserved so it handles daily holds limits

This patch implements the required changes in
C4::Reserves::CanItemBeReserved so it implements a daily limit on holds.

It returns the 'tooManyReservesToday' string if the policy doesn't allow
placing the hold. It returns 'OK' (current behaviour) otherwise.

To test:
- Run:
  $ sudo koha-shell kohadev
 k$ cd kohaclone
 k$ prove t/db_dependent/Holds.t
=> FAIL: Tests fail because the error condition is not making
CanItemBeReserved return the desired error code.
- Apply this patch
- Run:
 k$ prove t/db_dependent/Holds.t
=> SUCCESS: Tests pass!
- Sign off :-D

Signed-off-by: Séverine QUEUNE <severine.queune@bulac.fr>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>