use "rich" for terminal rendering

I'm thinking of replacing blessed with rich as a terminal rendering library. Rich is now mature and provides high level features that would be nice for us as we could drop a bunch of custom logic on our side. In particular:

• no more need to handle available vertical space to limit the number of processes rendered (the limit() decorator)
• automatic cropping or wrapping of long lines
• better handling of text split with terminal sequence (would allow to handle horizontal scrolling as suggested in #260 without loosing the formatting, or introducing a bunch of custom logic on our side)
• native table rendering
• "layouts" allowing to split the screen into multiple areas (possibly with fixed size, and automatic overflow handling)
• live display, allowing to refresh only part of the ui

That would be a large refactoring. But, after having played a bit with it, I think it's worth as it will make UI development easier long term.

Thoughts?

The issue names no files, tests, or entry points. Start by mapping the existing blessed-based terminal rendering implementation, then compare its responsibilities with Rich's cropping, tables, layouts, and live display; done would mean the terminal UI uses Rich while preserving the application's current rendering behavior.