Enhance remote UI protocol

[maks]

The protocol at the moment is an MVP. Extra features that would be nice to have for better UX are:

• send the actual colour of each cell as currently we only send the palette index of each colour
• alternatively a have way for a client to request the current palette index -> RGB colour mapping
• have a way for a client to request a resend of the current full screen
• send key presses to the client
• send to the client the current font in use