TUI setup

[matprec]

This implements a simple UI with the following features

• A thread selector (up + down)
• A message view, which displays recorded events, no nav currently

Closes https://github.com/tokio-rs/console/issues/4

[matprec]

@hawkw For you, most relevant is storage/*, this implements the actual subscriber/span handling

[matprec]

It currently relies on

• the tokio-trace/master, not the released version
• https://github.com/tokio-rs/tokio-trace-nursery/pull/59