* Introduce UserFriendlyError
* Replace newTranslatableError with UserFriendlyError
* Remove ITranslatableError
* Fix up some strict lints
* Document when we/why we can remove
* Update matrix-web-i18n
Includes changes to find `new UserFriendlyError`,
see https://github.com/matrix-org/matrix-web-i18n/pull/6
* Include room ID in error
* Translate fallback error
* Translate better
* Update i18n strings
* Better re-use
* Minor comment fixes