Save draft messages when switching channels

[BetaRays]

Is your feature request related to a problem? Please describe.
When switching to a different MUC or contact, anything I wrote in the entry box is lost.
Video demonstration

Describe the solution you'd like
When switching channels, instead of deleting the current draft message, it should be saved and restored when going back to the same channel. This should preferably be done in a way that would be saved in the browser local storage and survive a browser restart.
I don’t know where drafts should be saved in the code yet.

Describe alternatives you've considered
A (possibly) somewhat easier to implement option is to never delete anything from the text entry field, and keep the draft when switching channels, but I feel that this would be unexpected and unnatural for most users.

[BetaRays]

The maybeShow function and the ChatBox model might be of interest, but getting and setting the contents of the bottom text box should probably not be done in a headless plugin.