improve extension registry list UI

Created by: sqs

See commit messages for more details.

• Add categories and enabled/disabled filters to extension registry list.
• Remove extension titles; always use the extension ID. See the relevant commit message in this PR for the reason.
• Remove complexity around WIP extensions since #1508 will reduce the need for WIP extensions overall. (There were bugs here anyway; remote WIP extensions were still being shown even if includeWIP=false in the GraphQL query.)

Ready to review.