implement new 'zrepl status'

Primary goals:

- Scrollable output ( fixes #245 )
- Sending job signals from status view
- Filtering of output by filesystem

Implementation:

- original TUI framework: github.com/rivo/tview
- but: tview is quasi-unmaintained, didn't support some features
- => use fork https://gitlab.com/tslocum/cview
- however, don't buy into either too much to avoid lock-in

- instead: **port over the existing status UI drawing code
  and adjust it to produce strings instead of directly
  drawing into the termbox buffer**

Co-authored-by: Calistoc <calistoc@protonmail.com>
Co-authored-by: InsanePrawn <insane.prawny@gmail.com>

fixes #245
fixes #220

main.go

@@ -4,12 +4,13 @@ package main
 import (
 	"github.com/zrepl/zrepl/cli"
 	"github.com/zrepl/zrepl/client"
+	"github.com/zrepl/zrepl/client/status"
 	"github.com/zrepl/zrepl/daemon"
 )
 
 func init() {
 	cli.AddSubcommand(daemon.DaemonCmd)
-	cli.AddSubcommand(client.StatusCmd)
+	cli.AddSubcommand(status.Subcommand)
 	cli.AddSubcommand(client.SignalCmd)
 	cli.AddSubcommand(client.StdinserverCmd)
 	cli.AddSubcommand(client.ConfigcheckCmd)