Bug 15128 - Add ability to limit patrons open purchase suggestions

Bug 15128 - Add ability to limit patrons open purchase suggestions

To test:
1 - Define a number of MaxOpenSuggestions
2 - Add some suggestions for a patron
3 - Note they cannot add any more suggestions if limit is reached
4 - Delete a suggestion and note you can add another
5 - Add them to limit again
6 - Accept a suggestion in the staff client and note user can add more
7 - Repeat above with rejecting or deleting
8 - Sign off.

Sponsored by:
    North Central Regional Library (http://ncrl.org/)

Signed-off-by: Barbara Walters <bwalters@ncrl.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>