mail: Add khal configuration

Added configuration of khal calendar, making use of the previously set
up vdirsyncer configuration. It will dump calendar events into the
specified folder in documents, which will in turn be picked up by khal
and displayed. Any creations/edits can be synced back to the remote
Caldav server with vdirsyncer.

mail/.config/khal/config

@@ -0,0 +1,16 @@
+[calendars]
+
+[[calendar_local]]
+path = ~/documents/calendars/*
+type = discover
+color = auto
+
+[locale]
+timeformat = %H:%M
+dateformat = %Y-%m-%d
+longdateformat = %Y-%m-%d
+datetimeformat = %Y-%m-%d %H:%M
+longdatetimeformat = %Y-%m-%d %H:%M
+
+[default]
+default_calendar = Activities