#162: Add Postman Collection compiled for ICAT backend

- This is a Postman Collection I've built up over the past few months, containing 320 requests. The requests are aimed at the Python ICAT backend (with query params created for that backend) but can be used for the DB backend by changing parameters to SNAKE_CASE where needed. The collection has been exported as v2.1 and is ready to be imported into Postman