Bug 4045 - No check for maximum number of allowed holds.

Bug 4045 - No check for maximum number of allowed holds.

Re-add the system preference maxreserves.

All the code using maxreserves is still in place. Though it
is not used in the Reserves module, it is used in all the
scripts where holds are placed.

Also adds a check so that a borrower cannot exceed the maximum
number of allowed holds by using the multi-hold feature via
the opac.

Test Plan:
1) Apply this patch
2) Run updatedatabase
3) Set maxreserves to 3, set opactheme to bootstrap
4) Log into the opac as a patron
5) Place 3 holds
6) Attempt to place a 4th hold
7) Note you get an error message and cannot place a forth hold
8) Delete two of those holds
9) Attempt to place 3 or more holds as a multi-hold
10) You should see a warning that you cannot place this many holds
11) Try to anyway
12) You should see an alert to tell you to reduce the number of holds
    you are placing.
13) Reduce the number for holds you are placing to 2
14) Your holds should now be placed

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>