Chat settings UI to delete custom chains

[JasonWeill]

Problem

Once there is a UI to register new custom chains/actors for use in the chat UI (#273), we will need a way to delete these chains.

Proposed Solution

List all custom chains in the chat UI's settings. Let users delete these chains from the settings UI.

Additional context

Should we instead have a /list command in the chat UI that lists custom chains, and a /delete command that clears them?