Standardized Java Duration and their conversions (fixes #694).

[akara]

Merging all work from #706 as well as standardized the time conversion, especially from Java to Scala to retain the coarsest possible unit. For instance, a time of Duration.ofSeconds(120) will end up as 2 minutes in the FiniteDuration.

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[akara]

Closing this to prevent overriding #706. Rest of the fixes are in #716.