Use camelCase in resources for input test data

[danielfeismann]

          Could you replace the `_`?

Originally posted by @staudtMarius in #1132 (comment)

• Check all input.csv files e.g. src/test/resources/edu/ie3/datamodel/io/source/csv/_participants/cylindrical_storage_input.csv
• Remove the _
• Adapt tests

[danielfeismann]

After evaluating this further, we decided that this improment does not justify the amount of work necessary.