The License Expression editor only allows a maximum of two licenses per group

## Problem description

I want to edit the declared license to be:
```
MPL-2.0 OR MIT OR Apache 2.0
```
The License Expression editor does not let me do this - the "Add Rule" button does not work if there are two licenses in a group.

It appears that I can add another group and create a declaration:
```
MPL-2.0 OR (MIT OR Apache 2.0)
```
This is equivalent in terms of the logic, but adds unnecessary complexity, and may be confusing to consumers who may think there is some relevance to the grouping.

## Expected behaviour
To be able to add more than two licenses per group