pipe to calculate dates diff

[enriquezrene]

We need to have a pipe able to calculate the diff between two dates

pipe should be used as follows:

{ from_date | substract_date: substract_date }

The pipe will return the difference in hours and minutes.

2011-04-11T10:20:30Z | substract_date: 2011-04-11T08:00:30Z
will print in the UI
02:20

which is the difference between these 2 dates