Update solidity

[cabrador]

This PR relies on changes from #31 and #32 so those should be merged before reviewing this one.

This PR updates version of solidity to 0.8.27 and uses hardhat evmVersion cancun
It also makes all necessary changes that are required by this solidity version such as:

1. Using []bytes instead of []bytes32 for voting options
2. Adding virtual and override to some inherited methods
3. Correctly calling assembly methods
4. Using delete when wiping an array instead of setting its len to 0
5. Using memory instead of calldata in addTemplate in ProposalTeplates.sol due error Stack too deep
6. Using build-in openzepelin and/or funcs for type casting

[Mike-CZ]

LGTM