LP#1774427 Parse DoB dates as whole dates

LP#1774427 Parse DoB dates as whole dates

Fixes DoB parsing in the browser client patron edit interface by
creating date objects from a whole YMD date string instead of compiling
the date as collection of pieces.  Compiling dates from pieces (calling
setFullYear(), setMonth(), etc.) can have unexpected consequences,
because a change of month can result in a change of days as well, if the
number of days in the date object exceeds the capacity of the selected
month.

For example:

---
> d = new Date()
2018-05-31T14:59:26.186Z
> d.setMonth(1)
1520092766186
> d
2018-03-03T15:59:26.186Z
--

Parsing as Date(YYYY,MM,DD) instead avoids this kind of shuffling.

To test

[1] Log in to the staff client on the 31st day of the month :)
[2] Change a patron's DoB to a month that does not contain 31 days.
[3] Save patron and note on reload, the DoB shows the wrong value.

Signed-off-by: Bill Erickson <berickxx@gmail.com>