Make it configurable if calendars shows week numbers or not (closes #333)

public/viewjs/calendar.js

@@ -11,7 +11,7 @@ $("#calendar").fullCalendar({
 		"center": "title",
 		"right": "prev,next"
 	},
-	"weekNumbers": true,
+	"weekNumbers": Grocy.CalendarShowWeekNumbers,
 	"firstDay": firstDay,
 	"eventLimit": true,
 	"eventSources": fullcalendarEventSources

public/viewjs/components/datetimepicker.js

@@ -84,7 +84,7 @@ Grocy.Components.DateTimePicker.Init = function()
 			showToday: true,
 			showClose: true
 		},
-		calendarWeeks: true,
+		calendarWeeks: Grocy.CalendarShowWeekNumbers,
 		maxDate: limitDate,
 		locale: moment.locale(),
 		defaultDate: startDate,