This function identifies the format of a set of dates from a list of allowed formats.
findDateFormat(X, tz = NULL)
The date (given as a character string)
The time zone
It returns the date format, ready to use in the funtion strptime. If the dates have different formats, the function returns "variousFormats". If the format is not one of the allowed ones, it returns "notAllowedformat".
The allowed formats are: "%m/%d/%Y %H:%M", "%Y/%m/%d %H:%M","%Y-%m-%d %H:%M" and "%m-%d-%Y %H:%M"