i15-1: Provide an auto-assign on the puck mounting view

To make it easier for scientists to mount samples it would be useful for there to be an `auto-assign` button. This would take any unassigned pucks (in the selected visit?) and auto-assign them to empty spaces on the table. The scientist will still then need to press the mount button

## Acceptance Criteria
* We gather what empty locations there are on the table, from both ULIMS and the robot view?
* We allow users to select rows of the table for auto-assign (or all rows)
* When the user presses the auto-assign this will fill in the drop downs with empty positions

Start at the puck mounting view and trace how table rows, unassigned pucks, and empty locations are obtained from ULIMS and the robot view. The work is done when users can select rows or all rows, auto-assign unassigned pucks to empty positions, and see the resulting dropdown values before pressing Mount.

Written by the indexing model from the issue text.