Implement whispers between users

[fjallnari]

Currently users can only write messages either to the whole group, privately or to the GM only. Whispers could be added either a separate chat command or as another message mode to be cycled through. Some useful features would be:

• username autocomplete
• right-click on a specific user portrait in chat to pre-fill the whisper
• reply to the last whisper sent to user (maybe as a separate command in chat)

Sockets would need to be refactored a bit, #108 is a prerequisite.

[ptaranat]

We may want to consider limiting scope of a half-VTT to avoid implementing a full-fledged chat system. Currently, the language system (showing certain languages to PCs that can speak it) makes sense, as it is not something easily reproduced in Discord or other chat systems.

However, whisper functionality is well-represented in most chat systems through DMs or private "Aside" channels.

[fjallnari]

While I agree that implementing full-fledged chat system with mentions, emojis and what not is definitely out of scope for this project, whispers to me seem like a pretty basic feature (to not have the need to tab out for quick private messages).
I also think the main scope-limiting factor of a half-VTT should mainly be the lack of maps.

But this issue for sure is lower priority.