Add some native transformations for dateTime

[Seddryck]

It should be possible to transform a datetime to the corresponding datetime in UTC (assuming original value is local time) or local time (assuming original value is local time). If the original value is ambiguous (local time at the moment of the daylight saving from summer to winter) then the first hour is selected. User must specify the time zone Id or the name of one of the city listed in the display.
utc-to-local(Romance Standard Time)
local-to-utc(Brussels)

It should be possible to convert a datetime to a date (with time sets to 00:00:00).
dateTime-to-date

It should be possible to convert null to a constant date. If the field is empty and not null, the result is identical to a null field.
null-to-date(2018-01-01)

[Seddryck]

Beta available at https://ci.appveyor.com/project/Seddryck/nbi/build/1.19.0-beta.48.build.443