Add 'week_start' common option, mapped to dialog's --week-start option

* The value may be an integer or a string (cf. dialog's man page for
more details).

* Using this requires dialog 1.3-20160126 or later.

Author: frougon

dialog.py

@@ -405,6 +405,8 @@ def _simple_option(option, enable):
     "trim": lambda enable: _simple_option("--trim", enable),
     "version": lambda enable: _simple_option("--version", enable),
     "visit_items": lambda enable: _simple_option("--visit-items", enable),
+    "week_start": lambda start: _dash_escape_nf(
+        ("--week-start", str(start) if isinstance(start, int) else start)),
     "yes_label": lambda s: _dash_escape_nf(("--yes-label", s)) }