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/string_value_project/input-project/default.project.json

@@ -0,0 +1,12 @@
+{
+  "name": "string_value_project",
+  "tree": {
+    "$className": "Folder",
+    "on_file_system": {
+      "$path": "string_value.txt"
+    },
+    "inside_project_file": {
+      "$className": "StringValue"
+    }
+  }
+}