User input validation

[ErikKusch]

The current implementation of user input validation uses the Helper_InputChecker function which could use some improvements regarding:

1. Amount of space it takes up to specify it in each function that calls it
2. Error specificity when a mismatch is hit

[thisistaimur]

Issues:

• Standardization of function arguments.
• Error reporting.

Perhaps we should consider changing our json templates to Open Schem (https://schema.org) --> #8 .
Validation tools for validating agains schema:

• by creators of ajv: https://cran.r-project.org/web/packages/jsonvalidate/index.html
• validatejsonr: https://github.com/lejon/validatejsonr