Problem: Both in (typed) Morley and Lorentz `Contract` is used as the
name of a contract's code. However a contract also has more, for
instance annotations for parameter and storage (see `FullContract`).

Solution: 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.