I made some improvments. Please review and pull them.

These improvements and bug-fixes I have done:

improved: hiddenDate can also take an id of an existing input field,
which will be used instead creating a new one
improved: if defaultDate is set to true, it will take the Date in the
existing hiddenDate input field
bug-fix: under Firefox and Safari the String to Date parser doesn't
work with the format MM-DD-YYYY or YYYY-MM-DD . It has to be MM/DD/YYYY
or YYYY/MM/DD .