Import - Support for Alternate Date Field Formats

Currently, our Import logic (for both Contacts and Contributions) supports only the ISO 8601 format:

YYYY-MM-DD

I think it also currently supports the corresponding date+time format for fields that are type 'datetime' (PLEASE VERIFY as part of working on this issue):

YYYY-MM-DD hh:mm:ss (with and w/o seconds)

... and the compressed version of these:

YYYYMMDD hhmmss

Going forward we need to support the following alternative date input formats:

US dates -> mm/dd/yy or mm/dd/yyyy or mm-dd-yy or mm-dd-yyyy
(this is the default Excel output - at least for US versions)

and if not too difficult...
Posix default date style -> Mar 30 2002 (%b %d %Y)

So... we'll allow user to specify input date format for a given import session by adding a new radio button field to step 1 of the wizards:

Date Format: [ x ] yyyy-mm-dd [ ] mm/dd/yy [ ] mm/dd/yyyy [ ] Month dd yyyy (e.g. March 20 2005 OR March 20, 2005)