[Heatmap] Improve tick cadence with time scale

[markov00]

Is your feature request related to a problem? Please describe.
The current logic used to rarify the labels to avoid overlaps #1514 can be improved to support, whenever is possible, a nicer cadence with human recognizable time multiples, as using in the multi-layer time axis.

For example this can be converted to a 2 days intervals instead of 36 hours.

Describe the solution you'd like
When using a time scale with calendar intervals we should try to find a nice multiple of the specified unit.
for example with 1 day interval the allowed multiples are:
1 day, 2 days, calendar week, calendar month, 2 calendar months, 6 calendar months, calendar year, decade

with months and year, the tick cadence is not uniform but it will not probably be noticed much.