[WIP] Badge categories (resolves #330)

~~**Requires [streamsql #16](/brianloveswords/streamsql/pull/16) be merged before this will work.**~~

This is functionally complete, and can technically be merged as is (with the above caveat) - users can add categories to badges - but is missing any front-end flourish.

To do:
 - [x] Update `package.json` appropriately, ~~as and when the [streamsql pull request](/brianloveswords/streamsql/pull/16) is merged~~ *(required)*
 - [x] Allow users to add/remove input rows - currently, (at least) three inputs are provided
 - [ ] ~~Add admin option to edit category list~~