Selection no longer affects the mirroring point of symmetry

Instead, x_symmetry_point and y_symmetry_point are being used in Project.gd that determine the points of symmetry. This is necessary for #133

src/Classes/Project.gd

@@ -16,6 +16,8 @@ var guides := [] # Array of Guides
 
 var brushes := [] # Array of Images
 
+var x_symmetry_point := -1
+var y_symmetry_point := -1
 var x_min := 0
 var x_max := 64
 var y_min := 0