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/rbxm_fallback/input-project/default.project.json

@@ -0,0 +1,6 @@
+{
+  "name": "rbxm_fallback",
+  "tree": {
+    "$path": "src"
+  }
+}