Add bl_category to 3DView panel.

rigify/ui.py

@@ -198,6 +198,7 @@ class BONE_PT_rigify_buttons(bpy.types.Panel):
 
 
 class VIEW3D_PT_tools_rigify_dev(bpy.types.Panel):
+    bl_category = "Tools"
     bl_label = "Rigify Dev Tools"
     bl_space_type = 'VIEW_3D'
     bl_region_type = 'TOOLS'