ContractModel: wellformedness checks for Actions

[MaximilianAlgehed]

This PR introduces some checks that actions are well formed and don't refer to symbolic tokens that don't exist. A Data.Data based automatic predicate checks that no symtokens that aren't bound are used in actions and there is a possibility for the programmer to override this functionality with their own custom function (in case there is an issue with Data.Data). This means that issues like the one encountered in #342 don't affect developers and my "workaround" there isn't necessary.

Furthermore, this PR updates the dependency on plutus-core because we need instances of Data.Data for a number of types in plutus-core.

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  • Formatting, materialized Nix files, PNG optimization, etc. are updated
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[MaximilianAlgehed]

@sjoerdvisscher when you have the time this is ready :)