Support message withdrawal

[Xiangrui2019]

Describe the solution you'd like

When I send a message, if the message is filled in incorrectly, I can withdraw the message.

Describe alternatives you've considered

I have no alternative.

Additional context

Nothing.

[Anduin2017]

Under consideration.

[Xiangrui2019]

I think the message withdrawal function is quite useful, because if the wrong stream is sent, people want to withdraw, what should they do?

[Xiangrui2019]

I often fret about it when I use Kahla.

[Anduin2017]

Under consideration in this iteration. @l2dy How do you like this?

[Xiangrui2019]

why

[Xiangrui2019]

I've already made it. The basic idea is to add a new event, delete the message, and refresh the message list

[l2dy]

Why did you add the invalid label? @Xiangrui2019

[Anduin2017]

It was not about if you have made it or not. Kahla is an app which focuses on simple and secure. We need to make sure if this feature is worth and suitable to do in this iteration.

[l2dy]

The ability to delete messages from the server is a must for privacy reasons. But propagating the updates (message removal or edits) to other participants is another topic to discuss.