Added search for all lists on issue boards

## What does this MR do?

Adds a search box to allow the user to search all lists in issue boards rather than just the backlog.

## Screenshots (if relevant)

![Screen_Shot_2016-08-30_at_10.33.15](/uploads/67e96055d60a9b3209ce3831a1980c09/Screen_Shot_2016-08-30_at_10.33.15.png)

![Screen_Shot_2016-08-30_at_10.33.19](/uploads/8d5253b8f2ecf1cf9a69d70be8ccf1f9/Screen_Shot_2016-08-30_at_10.33.19.png)

## What are the relevant issue numbers?

Closes #21139

See merge request !6101