Contract subclass to handle link references

[njgheorghita]

What was wrong?

Contract factory subclass was needed to manage Package's which contain link references between, and adjust the bytecode accordingly.

How was it fixed?

Wrote a LinkableContract subclass that inherits from web3.contract.Contract. Implements following methods.

• has_linkable_bytecode
• link_bytecode
• is_bytecode_linked property

Cute Animal Picture

[njgheorghita]

@pipermerriam ready for an initial :eyes: whenever you get the chance

[njgheorghita]

@pipermerriam Thanks for the review! I beefed up the tests and got rid of the class mutation, let me know if there's anything else