Feature summary (what you would like to be able to do and where):
When creating round 1 for Montage only 1 single category is currently allowed. We would like more flexibility when merging multiple categories during round creation.

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
When a campaign would consist of multiple related campaigns they can't be easily loaded (merged via the tool).

We would either want to be able to mention multiple categories (like in e.g. WDFIST)
or, there could be a checkbox to allow to load subcategories as well
(could be limited to a number of levels, like in other category tools, like e.g. WDFIST).

Note also that currently the Montage file interface does not work, see T279386.
Otherwise we could have used AWB (AutoWikiBrowser) to merge the file lists manually into a list file, for each of the partial categories.

Benefits (why should this be implemented?):

• Easy to load multiple categories at one time, via the application "create round 1" form.
• No manual work to perform.
• Avoiding mistakes.
• Avoid data loss.