temporaldummy method implementation

[config-i1]

Implement the following options for POSIXct:

1. type="hour", of="week" - currently it assumes that the data is hourly;
2. type="minute", of="week" - currently it assumes that the data is in minutes;
3. type="minute", of="day" - currently it assumes that the data is in minutes;
4. type="halfhour";
5. type="second", of!="minute" - only minutes are available for "of" at the moment.

Also, implement methods for the classes:

1. xts
2. tsibble
3. timeDate / timeSeries