[#12] rename Contract to ContractCode

Description

As advised in the issue, the solution is split in two parts:

• rename Contract to ContractCode
• rename FullContract to Contract

This solves the first part of the problem and renames both the typed Morley's and Lorent's Contract to ContractCode. Additionally convertContract and printTypedContract also have been renamed because their FullContract counterparts already exists and those will be renamed to these ones.

Related issue(s)

Part of #12 (closed)

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