Feature Request: date conversion and add functions

[InverseFalcon]

Most of APOC's date/time functions deal with parsing a timestamp (at some time resolution) from a string, and formatting to go the other direction.

APOC could use some additional date functions for converting a timestamp between different resolutions, and adding/subtracting some amount of time at a specific resolution (though keeping the output at original resolution).

Some possible functions:

apoc.date.convert(<timestamp>, <timestampResolution>, <desired resolution>)
example usage:
return apoc.date.convert(timestamp(), 'ms', 'd') as todayInDayResolution

apoc.date.add(<timestamp>, <timestampResolution>, <numberToAdd>, <addResolution>)
example usage:
return apoc.date.add(timestamp(), 'ms', -3, 'd') as threeDaysAgoInMs

[jexp]

Thanks a lot @InverseFalcon !