WIP: fixCompiler Warnings

This does not change any code, but it uses new solidity features to be more precise and to fix warnings from the compiler.

• use constructor instead of the contract name
• use blockhash instead of block.blockhash
• use abi.encodePacked as keccack25 only takes a single bytes argument now, so we have to tightly pack them.

THis is marked as WIP, because 'scripts/create2concepts2assessments.js' will stop working as soon as our code uses the new constructor()-methods, see #234 (closed)