Rewrite of ABI and Contract parsers

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In the beginning, I went ahead and build ABI/ContractInfo parsers by utilizing antlr-go parser directly. Idea was to have these parsers available at will.

This approach is good if you need only ABI or ContractInfo from any specific contract, however, it's a very bad design if you need AST, Contract and ABI including any future solutions such as IR or SMT.

Right now each listener will re-parse the entire tree for all of the packages stated above. Therefore, I suggest to use AST parser to parse the source code once and modify abi and contracts packages to build results based on AST tree layout.

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This is now completed.