Redesign UI toast

[Kruithne]

The current toast implementation is not great, it's a static message which can be overwritten by any other message. Ideally, it should become a stack system where, either, one of each type (error, info, etc) can exist and are displayed together, or any amount of messages can be pushed to it, but they are ordered by priority (error is higher than info).

Discuss the best way to implement this.