Modify GEDCOM importer to support before/after/between dates for event dates

[stangel]

Depends on https://github.com/geni/geni/issues/463 -- @ss can provide the API format once it's done.

[stangel]

/assign @Raynes

[scott-steadman]

https://github.com/geni/geni/issues/463 is done.
The API already supported it. I just added tests to make sure.

date hashes are now like this:

{
  'year' => nnnn, 'month' => nn, 'day' => nn,
  'range' => 'before|after|between',
  'end_year' => nnnn, 'end_month' => nn, 'end_day' => nn
}

end_year|month|day are only needed if range is 'between'