LP1983156 Consolidate Unified Holdings preference, Make buttons more

LP1983156 Consolidate Unified Holdings preference, Make buttons more
explicit

The single preference "Unified Holdings, Item Attributes Display, and
Item Templates" controls display and template content.

Renames buttons to avoid confusion as follows:

Apply -> Apply Template
Save -> Save Template
Import -> Import Templates
Export -> Export All Templates

Signed-off-by: Michele Morgan <mmorgan@noblenet.org>
Signed-off-by: Jane Sandberg <sandbergja@gmail.com>
Signed-off-by: Terran McCanna <tmccanna@georgialibraries.org>