changed usage of code as identifier.

[nishant-sachdeva]

We're currently implementing immutable for dynamic types in the compiler. With things like arrays and structs, however, it's much more tedious to enforce the immutability at contract construction time (and not everyone even thinks that this immutability is desirable) so we decided to make them freely writable at that stage instead. To make this clear we're introducing a new keyword: code. This is a breaking change so it will only really become a keyword in 0.9.0.

Turns out that colonyNetwork has one instance of code being used as an identifier. This PR changes its name for future compatibility and also will help us test the compiler against colonyNetwork without having to maintain a fork just for this small tweak.

[CLAassistant]

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[kronosapiens]

@nishant-sachdeva thanks for letting us know! Can you sign the CLA so we can move forward with the review?

[kronosapiens]

Making a note to check with front-end about whether they reference the code variable by name.