Xontrib-prompt-bar

Fix `env_name` stripping.

Using `YELLOW` for exit code `-2` (`Ctrl+C` in Linux)

* Added printing return code (can be disabled by `XONTRIB_PROMPT_BAR_SHOW_RETURN = False`)
* Fix `screen` section to avoid https://github.com/xonsh/xonsh/issues/4912

Fix background.

Temporary fix: `gitstatus` was removed.

Cleaning.