lp1691237 webstaff: fix Format Dates and Format Times

lp1691237 webstaff: fix Format Dates and Format Times

This change deprecates the existing Format Dates and Format Times settings
and adds two settings for use with the webstaff client:

    Format Dates with this pattern
    Format Date+Time with this pattern

These settings use format strings as documented here:

https://docs.angularjs.org/api/ng/filter/date

There is overlap with how the Dojo formats worked, but also some differences.

The original Format Dates and Format Times settings worked together, but the
new settings work independently.  Certain field elements will use one, and
certain field elements will use the other.  These distinctions are hard-coded
in the various UI templates, with the idea being that timestamp fields in
which the date component alone is sufficient information (for example, DOB)
will use the Format Dates setting.  Fields where the time component is
important (for example, Checkout Time) will use the Format Date+Time setting.

When the settings Format Dates and Format Date+Time are unset, we will default
to "shortDate" (M/d/yy) and "short" (M/d/yy h:mm a), respectively.

Signed-off-by: Jason Etheridge <jason@equinoxinitiative.org>