Replace parsePikadayDate with newDate

What does this MR do and why?

This MR removes parsePikadayDate in favour of newDate whose name isn't tied to a library like pikaday, to be more generalised. parsePikadayDate only accepts yyyy-mm-dd string formats, and newDate which replaces it contains the same logic.

This is the final MR of a series which included !167792 (merged) and !168085 (merged).

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