Wrap conversion exceptions in a ValueConversionException

To help provide better error reporting to users wrap the
conversion exception into another providing the column or
property that the conversion failed on. This allows for both the
column and row causing the issue.
Please move the message into the exception class. See [this one](https://github.com/ddeboer/data-import/blob/master/src/Ddeboer/DataImport/Exception/UnexpectedTypeException.php), for example.