Drop rows that fail validation

[felix-oq]

Part of #58

Changes the implementation of LayoutValidator such that rows are dropped if they fail validation. To achieve this, the implementation was changed to a row-wise instead of a section-wise validation.

I also changed the grammar so that row sections can only be used to describe CSV headers because it simplified the implementation and I could not think of a reasonable use case where that would be needed.

Additionally I surrounded column names with " in the generated SQL statements which solves the error mentioned in #58.

The gas example now runs successfully while logging any validation errors that occurred. The resulting DB table only contains the first non-header row of the CSV file because all other rows miss some values and thus fail validation.

[rhazn]

I am not sure how I feel about the more restrictive solution regarding rows... I am sure there is data out there where this will be an issue. But I think we can iterate on it when we actually encounter that data.

The other changes are great of course 👍 .