* 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
* Add support for overriding strings in the app
This is to support a case where certain details of the app need to be slightly different and don't necessarily warrant a complete fork.
Intended for language-controlled deployments, operators can specify a JSON file with their custom translations that override the in-app/community-supplied ones.
* Fix import grouping
* Add a language handler test
* Appease the linter
* Add comment for why a weird class exists
Michael Telatynski