[Feature] Support for Set mapping in the template schema

[Udayraj123]

The template schema has introduced a new key conditionalSets to handle conditional field block layouts.

• This will be useful to support different test paper sets based a common position of the test code/booklet code/set code field
• The format string should have access to all fields read from the default field blocks layout, and also the filepath
  • See if we can close #145 using filepath as a field in formatString
• In future when custom fields like Barcode are supported, we can use the same schema to map each barcode/QR code to a different test layout within a single template.json file
• We have already separated out FieldBlocks handling in a separate class from the Template class to facilitate this relatively easily.
• Similarly the evaluation schema also has the conditionalSets key to enable different answer keys for the different sets of questions.

[Udayraj123]

To be closed after https://github.com/Udayraj123/OMRChecker/issues/190 is fixed and is stable.