Make the Encryption optional

[casaout]

As we are still working on a guide to analyze the encrypted database files, I'd like to make this feature optional (disabled by default) so the researcher can set it in the study.config.ts file.

Changes:

• Please add a property dataExportEncrypted (default: false)
• Update the exporter to consider the property
• Hide the text on the last page of the exporter about the encryption