enable use of alternate period classes

'firstWeekday' code removed
Week0 provides a Week period that begins on Sunday -
to use it pass array('weekClass' =>' \Calendar\period\Week0') to Calendar::setClasses().
if instantiating Month directly, pass array('weekClass' =>' \Calendar\period\Week0') to Month::__construct as second parameter.
modify to use PeriodFactory
Merge branch 'alt-period-classes3' into alt-period-classes

Conflicts:
	src/CalendR/Calendar.php
	src/CalendR/Period/Day.php
	src/CalendR/Period/Month.php
	src/CalendR/Period/PeriodAbstract.php
	src/CalendR/Period/Range.php
	src/CalendR/Period/Week.php
	src/CalendR/Period/Year.php
	tests/CalendR/Test/Period/AlternatePeriodsTest.php
modify to satisfy FirstWeekDayTest