Declare atom.hasTiledEditor = true

This way packages that are affected by relative coordinates will be
able to smoothly upgrade using a feature toggle.

src/atom.coffee

@@ -34,6 +34,8 @@ class Atom extends Model
     atom = @deserialize(@loadState(mode)) ? new this({mode, @version})
     atom.deserializeTimings.atom = Date.now() -  startTime
 
+    Object.defineProperty(atom, "hasTiledEditor", value: true)
+
     if includeDeprecatedAPIs
       workspaceViewDeprecationMessage = """
         atom.workspaceView is no longer available.