Write JSON deserializers for Reference, Constructors, Items and Data.

This is needed in order to deserialize a JSON blueprint and use it to perform validation.
  Still TODO:

  - [ ] Write JSON deserializer for 'Schema'

  Which should now be relatively straightforward.

crates/aiken-project/Cargo.toml

@@ -37,3 +37,6 @@ toml = "0.7.2"
 uplc = { path = '../uplc', version = "0.0.29" }
 walkdir = "2.3.2"
 zip = "0.6.4"
+
+[dev-dependencies]
+proptest = "1.1.0"