Make appearance.calendarview more explicit in config file

Instead of using 0 or 1 as a value for `appearance.calendarview`,
introduce the more explicit "monthly" and "weekly".

Also update `scripts/calcurse-upgrade.sh` to reflect the change.

Signed-off-by: Baptiste Jonglez <baptiste--git@jonglez.org>
Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/calcurse.h

@@ -360,6 +360,13 @@ struct recur_event {
   char *note;                   /* note attached to event */
 };
 
+/* Available view for the calendar panel. */
+enum {
+  CAL_MONTH_VIEW,
+  CAL_WEEK_VIEW,
+  CAL_VIEWS
+};
+
 struct notify_app {
   long time;
   int got_app;