Storage root to detect new collator set in Tanssi chain

[girazoki]

Once #51 and #52 are done, we need to detect the Tanssi storage root in the pallet and create a proof against it that containerChain collators build. This storage proof should be retrievable, as the client now has access to the state of both chains (tanssi and the relay)

[girazoki]

Actually this can be done without #51 in place. We could simply require to insert the authorities based on assignation, we can detect the assignation on the client side later