Add option to pad with 0s

[Bergam0t]

Some data you use in PowerBI may benefit from having an option to turn on or off putting in a 0 for date points that have no data.

e.g. if monthly data put in, for months with no data, put a 0 in for that month instead.
Similar for daily.

At the moment it just jumps to the next time data is present, which is going to cause incorrect calculation of limits/incorrect behaviour.

[Bergam0t]

Initial attempt made in #68ff385
Tries to guess what the intended time between points should be. I'm not sure these calculations are particularly robust but seem to be working relatively well for my test data.
Would be good to add in additional option to either take the automatic guess at the intended intervals or overwrite with some common ones - month start, month end, day, week, year?