Processing of data files

- As a researcher, I want to be able to see all important files and if needed all variable names belonging to a file : There should be a button with “list imported data files”
- As a researcher, I want to select a specific data file for further processing: From the listed imported data files, a file can be selected for further processing by clicking on it.
- As a researcher, I want to be able to select a variable for further processing. If a variable has been selected, different options for labelling are available. one option can be selected per variable: From the list of variables, a variable can be selected for further processing by clicking on it.  A list of options appears, from which one can be selected. The list covers, “primary outcome”, “secondary outcome” and “intervention”