We need to add another pair of parenthesizes when propagating an
initialization of ItemListModel, because a comma in a template argument
would work as a separator of macro arguments, leading to a compile
error.
In some calendars, weekends start on other days than saturday and can
also have different lengths than 2 days. This patch allows you to set
these values, however they don't do anything yet as Serenity's Calendar
doesn't care about Weekends at the moment.
