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>
Bug 10515: add regression tests

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Bug 10515: (follow-up) fix use of GetBranchCategories

Adjusting to reflect the removal of the branchcode parameter
to GetBranchCategories; also filter on the 'searchdomain'
library group type, as appears to have been intended.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>