Implement Syncback to support converting Roblox files to a Rojo project (#937)

This is a very large commit.
Consider checking the linked PR for more information.

rojo-test/syncback-tests/unscriptable_properties/input-project/default.project.json

@@ -0,0 +1,9 @@
+{
+  "name": "unscriptable_properties",
+  "tree": {
+    "$className": "BinaryStringValue"
+  },
+  "syncbackRules": {
+    "syncUnscriptable": true
+  }
+}