Bug: Fixed output separator causing Excel conversion issues

[berntpopp]

Description:

The current fixed output separator in the select fields section is a comma ,, which can cause issues in Excel (e.g., 42,1,120,23 being converted to a number). The script should change the standard separator to something else (e.g., |) and allow setting this as a parameter. The same applies to the NA value.

Steps to Reproduce:

1. Run the script and observe the output with fields containing multiple values separated by commas.
2. Open the output in Excel and notice that the fields are incorrectly interpreted.

Expected Behavior:

The script should use a different standard separator (e.g., |) and allow users to set the separator and NA value as parameters.