Bug 10515: make behavior of library category fetchers consistent with other fetchers

Bug 10515: make behavior of library category fetchers consistent with other fetchers

The prototype is not consistent, GetBranchCategory should return only 1 result
and GetBranchCategories should not have a categorycode argument.
This patch fixes that.

Test plan:
1/ Try to add/remove/modify a library.
2/ Add some groups
3/ Add these groups to a library

Signed-off-by: Srdjan <srdjan@catalyst.net.nz>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit ec3735433aed8d2c1a42b7d0758b4405a3aa6b1c)
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>