Allow input CSV file in SemApps importer

**Problem
For the moment, we can import only JSON files with SemApps Importer (via getAllFull).

**Proposal**
It would be great to allow CSV files too.

**Alternatives**
Two way to do that, make a specific importer for CSV file, or add a parameter to Importer mixin (ex : source.fileType).

The issue names the Importer mixin and getAllFull; start by locating those entry points and checking how JSON input is parsed. Review the existing importer tests or import path, then determine which proposed CSV approach fits; done means CSV files can be imported through SemApps.

Written by the indexing model from the issue text.