Implement ISO 8601 Durations for preview and pastview

[naimo84]

Durations define the amount of intervening time in a time interval and are represented by the format P[n]Y[n]M[n]DT[n]H[n]M[n]S or P[n]W

• P is the duration designator (for period) placed at the start of the duration representation.
  • Y is the year designator that follows the value for the number of years.
  • M is the month designator that follows the value for the number of months.
  • W is the week designator that follows the value for the number of weeks.
  • D is the day designator that follows the value for the number of days.
• T is the time designator that precedes the time components of the representation.
  • H is the hour designator that follows the value for the number of hours.
  • M is the minute designator that follows the value for the number of minutes.
  • S is the second designator that follows the value for the number of seconds.

For example, "P3Y6M4DT12H30M5S" represents a duration of "three years, six months, four days, twelve hours, thirty minutes, and five seconds".
https://en.wikipedia.org/wiki/ISO_8601#Durations