Journaling support

[corrideat]

Problem

@chelonia/lib 1.4.4 adds an optional event journal that can be used for debugging purposes. The journal is already enabled in #2961.

However, #2961 is an extremely basic implementation that's missing crucial UX features:

1. The journal has support for redacting certain information from the state, which Replace runtime with chel serve #2961 is not using. Since many parts of the contract state contain potentially sensitive information (e.g., actual messages sent by users), we might want to define which redactions to apply.
2. More crucially, the journal is only accessible programmatically, and there's no way to obtain it from the UI. This is an important limitation because it requires users to use development tools to get to the journal for making a report, which can be difficult (users may not be familiar with these tools, scary warnings are (justly) shown before pasting code) or impossible to get (e.g., development tools may be unavailable in certain browsers, especially on mobile, or might require even more special tooling, such as Android Bridge or Xcode).

Solution

1. Decide which fields should be redacted and how, then implement these redactions.
2. Add an option to the UI to export contract journals, similarly to how now we can export app logs (perhaps it could be a combined logs + journal export).

[taoeffect]

Decide which fields should be redacted and how, then implement these redactions.

• Private keys by hashing them and spitting out the first 6 characters of the hash.
• Chatroom messages by replacing them with xxxxxxxx or something to that effect.
  • Same for Pinned Messages

Add an option to the UI to export contract journals, similarly to how now we can export app logs (perhaps it could be a combined logs + journal export).

Seems like combined { "logs": [ ... ], "journal": [ ... ] } makes sense to me.