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

docs/changelog.rst

@@ -31,6 +31,12 @@ We use the following annotations for classifying changes:
 -----
 
 * |break| Change syntax to trigger a job replication, rename ``zrepl signal wakeup JOB`` to ``zrepl signal replication JOB``
+* |feature| New ``zrepl status`` UI:
+
+  * Interactive job selection.
+  * Interactively ``zrepl signal`` jobs.
+  * Filter filesystems in the job view by name.
+  * An approximation of the old UI is still included as `--mode legacy` but will be removed in a future release of zrepl.
 
 0.3.1
 -----