[Java] Support additional Date metadata

[asfimport]

The Date type format from ARROW-316 introduced a DateUnit

Reporter: Bryan Cutler / @BryanCutler
Assignee: Bryan Cutler / @BryanCutler

Related issues:

• [Java] Add Date/Time Support to JSON File (is depended upon by)

_{Note: This issue was originally created as ARROW-701. Please see the migration documentation for further details.}

[asfimport]

Bryan Cutler / @BryanCutler:
I could give this a shot

[asfimport]

Bryan Cutler / @BryanCutler:
PR: #431

[asfimport]

Julien Le Dem / @julienledem:
Issue resolved by pull request 431
#431