Cycle analytics: deltas between cycles
#### Description
We should display the deltas between cycles.
#### Specification
* Delta: difference between the previous cycle and the current one (whatever is selected in the date picker).
* Deltas are expressed in human readable format, like "-4 days" or "+4 hours"
Instead of the little triangle we should just call it `Change` and in the ? specify that it's vs the previous period of the same time

issue