implement two more input fields in drago registry for external storage

[gabririgo]

implement the following two fields, in order to use external storage services for data for dapp:

bytes32 ipfslinkhash bytes32 swarmlinkhash

double check whether it fits into stack depth and implement asap. It is a good excercise with the dragos, where the stack depth is very ofter an issue

[gabririgo]

in the registry, we already have a function to add metadata to a pool, hence it is not controversial that bytes32 types can be added.