Bug 5811: Add sysprefs to control overriding fines

Bug 5811: Add sysprefs to control overriding fines

This patch adds two sysprefs to allow libraries more fine-grained control over
when fines can and can't be overridden. The two sysprefs are:
* AllFinesNeedOverride - when this syspref is set to "Require" (default) any
    fine will require a staffmember to override the fine in order to check out a
    book.  When set to "Don't require," fines below noissuescharge will not need
    any override.
* AllowFineOverride - when this syspref is set to "Allow," staff will be able to
    override fines that are above noissuescharge. When set to "Don't allow"
    (default), staff will not be able to check out items to patrons with fines
    greater than noissuescharge.

Signed-off-by: Nicole C. Engard <nengard@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>