NightlyBase doesn't convert string in dayOfWeek param

No conversion is made of the value in dayOfWeek if it's a string. The
value is directly passed to croniter without proper conversion.
This fix handles both single string values and multiple comma separated
values as well as abbreviation in the string. ("0" "5,6" "0,fri" et.c.)
If it's not a valid value I hope that croniter will handle that. I thought that it would be better handled by croniter than me doing some extra checks.
I just want to be sure that integers are converted to croniter compatible values so schedules doesn't start one day early as they do now.