Add option to bulk validation using csv files

[Aadesh-Baral]

Add option to bulk validate using csv file. For this we need a feature to let users download the features in the challenges in the csv format on which users can add a field with name is_valid and upload back to the application. And if the value is set True, yes or y then set the feature as valid and if the value is set False, no or n set the feature as invalid.