Change JSON model naming behavior.

- JSON model names now come from the file name
- The 'Name' field is now optional for the top-level instance
- Snapshot tests run way faster by executing Rojo directly instead of Cargo

rojo-test/Cargo.toml

@@ -8,4 +8,7 @@ publish = false
 [dependencies]
 insta = "0.10.0"
 paste = "0.1.5"
-tempfile = "3.1.0"
+tempfile = "3.1.0"
+
+# We execute Rojo via std::process::Command, so depend on it so it's built!
+rojo = { path = "../server" }