(Collateralized Channel) Smart Contracts need update to Solidity

[NhoxxKienn]

This is related to #17

Context

The update from Go-perun 0.6.0 to 0.10.6 leaves the old custom smart contracts not compatible anymore with the newest version of smart contracts from the perun-eth-backend. To have the test running again, these smart contracts will need to be upgraded to solidity 0.8.0 and must be compatible with the newer perun-eth-contracts.

Goal

We want to test, review, and, if necessary, update the code of the demos smart contracts to ensure compatibility with go-perun 0.10.6

Note

The script to generate go bindings has already been updated to the newest solc just like in the app-channel.