Adding LocalDateTime Support via Extensions (Issue #100)

[Shounaks]

relates to #100

[cowtowncoder]

This looks like a good starting point, but one quick note: instead of adding code to existing Maven sub-projects (general jr-objects, annotation-support), this would need to be a new sub-project/module.

Like jr-extension-datetime (for example). It'd depend on jr-objects and could be depended on (and registered) by projects that need it.
I'd prefer this over adding limited functionality in core; this allows plugging alternate implementations, and publishing new versions of datatype extensions quicker if necessary.