Field name validation

## Background
If a field name for standardization is not valid for _parquet_ format, the whole standardization is executed and the process fails on saving to _parquet_ file.

## Feature
It would be much more efficient to verify the column names as part of the verification at standardization start and fail early.

## Proposed Solution
Possible places to do the validation at:
* `SchemaValidator` object
* `FieldValidator` class

Start by inspecting the `SchemaValidator` object and `FieldValidator` class to determine where standardization-start verification is performed. Reproduce the invalid parquet field-name case, then add validation before standardization proceeds and verify that invalid names fail early rather than only when saving the parquet file.

Scritto dal modello di indicizzazione a partire dal testo della issue.