LP#1464767 Browser client scrollable selectors

LP#1464767 Browser client scrollable selectors

Adds a new scrollable-menu CSS class.  It's (provisionally?) limited to
larger screens, w/ the assumption that smaller screens handle scrolling
for you.

New class is applied to org unit selects only so far.

Signed-off-by: Bill Erickson <berickxx@gmail.com>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>
Conflicts:
	Open-ILS/src/templates/staff/css/style.css.tt2

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>