Frontend for supporting categories as inputs from users. Tasks for this ticket:
- Add an accordion section for "Categories" under the current "Participants" accordion.
- Below the heading is some help text for the section: Event data would be generated by counting participant edits in the specified categories. If no participants are specified, all edits to the category during the event will be counted.
- Add a blank text input for category name and a dropdown for wiki next to it, by default.
- The 'wiki' dropdown contains the wikis the user picked for the event. In the case of *.wikipedia, it would contain all wikipedias and so on. The wikis appear in the list by their full name - English wikipedia, German wikisource etc.
- Add a button to allow user to add more inputs as above. This behavior is similar to how adding Organizers works. When the ➕ button is clicked, a blank text input is added for the category and a dropdown wiki input is added with the same wiki as the user last picked.
Note that subcategories in the mock will be added in T200481: Allow for subcategories to be included when parsing categories.