Implement vim-like commands in footer

[ihabunek]

Proof of concept, supports only :quit and :help.

[ihabunek]

@danschwarz Playing around with vim style commands. This PR is a proof of concept, only implements :quit and :help. If you have some time check it out and see if it works well.

[danschwarz]

Works fine; consider adding

self.tui.loop.set_alarm_in(3, lambda *args: self.tui.footer.clear_message())

after

self.close(False, f"Unknown command: {command}")

[danschwarz]

Works fine and should be expanded.

Right now there are a lot of key bindings, some are non-intuitive. Could move the less frequently used commands to the vim interface and get them out of the key bindings.

Consider adding

self.tui.loop.set_alarm_in(3, lambda *args: self.tui.footer.clear_message())

after

self.close(False, f"Unknown command: {command}")