CANCELED - New features for the TranscriptWindow and TranscriptWindowInterceptors

[cdanger]

• Enable TranscriptWindowInterceptors to apply different background/foreground colors - and more generally different styles - to different parts of a message text displayed in the TranscriptWindow, using the syntax of Asciidoc Custom Inline Styles ( https://docs.asciidoctor.org/asciidoc/latest/text/custom-inline-styles/ ), i.e. '[.style-name]#my styled text#' will apply the style 'style-name' to the text between ''#' characters.

• Enable TranscriptWindowInterceptors to intercept messages that were added to a chat before the user joined the chat.

• Fixed the issue in chatrooms that if the message is coming from the chat server (e.g. the server rejected the message for security reasons) and not a room occupant, an exception is thrown and the message is not displayed in chat window.

[stokito]

The new styling feature is not compliant with XEP-0393: Message Styling which is a small subset of Markdown. So no any other clients will support it, but that should be fine for the Spark that is mostly used to talk with other Spark clients.
From a practical perspective... Users probably won't use it manually as other MD tags. They'll need for a WYSIWYG editor.
Bringing syntax from the Asciidoc brings a question of other features and eventually will end with a conflict with the MD.

Usually, for the advanced styling was used XEP-0071: XHTML-IM but it has own problems.

I'll check the PR later and will think what can be done

[cdanger]

I messed up the PR branch when trying to resolve the conflicts, so I re-created a new clean PR for this: #960 . Sorry for the inconvenience.