[Java] Change the "boxed" object representation of date and time types

[asfimport]

This is follow on work to ARROW-729 per discussion in #475

Reporter: Wes McKinney / @wesm
Assignee: Leif Mortenson / @leifwalsh

Related issues:

• Arrow 0.3 release (blocks)

_{Note: This issue was originally created as ARROW-768. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Resolved in f4fcb42