Implement 'seriesP . seriesF @AnyList ≡ id' testing property

[chshersh]

After #60 and #63 is done we can implement such property. Though it's really difficult to implement this as it seems to me...

1. We need to somehow generate random type-level list of time units.
2. We need to think of a way to make seriesF result actually meaningful. We don't want to generate 1234 picoseconds and format this with lists [Hour, Minute, Second] very often.

• [x] unitsF and unitsP
• [ ] Think how to generate random list of types

[chshersh]

I think for now we can just have tests with unitsF and unitsP and only much later think on more sophisticated tests.

[chshersh]

For generating random type level lists we could use trick suggested in this tweet:

• https://twitter.com/DiazCarrete/status/962679579969191936