LP1760599: Only show merge records action when multiple bucket records selected

LP1760599: Only show merge records action when multiple bucket records selected

To test:
1) Create a bucket.
2) Select one record from your bucket. Right-click on your record or click on the Actions drop-down.
3) Note that "Merge Selected Records" is clickable.
4) Apply this commit.
5) Repeat steps 2-3.  Note that "Merge Selected Records" is no longer
clickable, unless you select two or more records.

Signed-off-by: Jane Sandberg <sandbej@linnbenton.edu>
Signed-off-by: Rogan Hamby <rogan.hamby@gmail.com>