LP 1889628: SIP2 Patron Username Lookup

LP 1889628: SIP2 Patron Username Lookup

Allow SIP2 clients to pass the username or barcode in the SIP2 Patron
Identifier field (AA).

To make this possible, we modify the OpenILS::SIP::Patron->new method
to accept a usrname key to retrieve patrons by usrname.

We also modify the OpenILS::SIP->find_patron method to accept a
usrname key to look up patrons.  The find_partron method is further
modified to check the patron id against the opac.barcode.regex in more or
less the same manner as the OPAC.

Two helper functions are added to OpenILS::SIP:

1. get_ou_setting: to retrieve org unit settings using the home_ou of
the logged in SIP2 account.

2. get_barcode_regex: To retrieve and cache the opac.barcode_regex
setting.

Signed-off-by: Jason Stephenson <jason@sigio.com>