Make GetTimePeriod() and others accept days.

Make GetTimePeriod() and others accept days.

GetTimePeriod() was written to take a month
('YYYY-MM') and work with that. Make it accept
not only a month, but also a day ('YYYY-MM-DD')
by adding a $TYpe modifier.

Rename LastMonth() to LastMonthDay() and rewrite
it accordingly.

Rename CheckMonth() to CheckPeriod() and rewrite
it accordingly.

As GetTimePeriod() defaults to 'month' if no
modifier is passed this change should be backwards
compatible.

Signed-off-by: Thomas Hochstein <thh@inter.net>