Add configuration options which data values are interpreted as boolean values

Problem:

Possible values of answer data given in the CSV file can be manifold (e.g. y|Y|yes|Yes|YES|n|N|no|No|NO|true|True|TRUE|false|False|FALSE|on|On|ON|off|Off|OFF). On top, these values of valid boolean values may also change depending on the survey tool used.

Solution:

We would like to give a list of "true values" and "false values" while reading in CSV data. Hence, we need a configuration option somewhere where we can specify these values.

Options:

1. Either we leave it as it is as a note in the code or
2. we put the information redundant next to each boolean question or
3. we have a configuration section in the metadata or
4. we put it into the settings file as a central place for configurations or
5. we put it in a separate configuration file read in by a configuration class/module or
6. we put two lists next to "AnswerType" in class Answer or
7. we allow the user to specify his intentions via CLI.

Choice:

• As a first suggestion we go for a combination of option 3 and 4.
• We would like to reserve an optional section in the metadata file for specifying these truth values and give default values in the settings module for the case that no values are given in the metadata file.