enable CSV Reader to ignore invalid lines like an empty line at the end and comments - FLINK-1208

Corresponding to issue FLINK-1208:
enable CSV Reader to ignore invalid lines like an empty line at the end, multiple header lines or comments without throwing an exception
These modifications change Flink's behavior for any type of InputFormat, not just CSVInputFormats.
If we want to allow to skip invalid lines, this is not the right place to add this feature.