Better error reporting for CSV Upload function

[ptomasula]

While addressing InfluxDB related dependency issue, I refactored the CSV upload method (/api/data-file-upload/) to have better exception handling. Exceptions (if encountered) are now tracked in a list and a 206 response will be returned along with the errors list.

Additional work is needed on the front end of the application so that it can better leverage this 206 response and generate an error report. Currently the 206 response is processed as a completely successful upload and the additional error information is not passed to the user.