Fix unicode-related failures in CSV upload.

TNL-586

@adampalay 
Something like:

```python

def _get_utf8_encoded_rows(self, rows):
    """
    Given a list of `rows` containing unicode strings, return a
    new list of rows with those strings encoded as utf-8 for CSV
    compatibility.
    """
    # return [[unicode(s).encode('utf-8') for s in row] for row in rows]
    for row in rows:
        yield [unicode(s).encode('utf-8') for s in row]

```