Unknown message types are not displayed

[Ralith]

Per the m.room.message spec, the "body" key of message event content

MUST be used with every kind of msgtype as a fallback mechanism for when a client cannot render a message.

Nheko thus can and should display the contents of this key to the user as plain text for unrecognized messages.

[mujx]

Just to keep track of the missing messages

• m.video
• m.audo
• m.location

[Ralith]

To be clear, this is not a problem of missing handling for specific message types. This is a problem of missing handling for otherwise unhandled message types, and is needed regardless of what message types are handled.