remove uv modifier from bld_mesh.py and finish flatten uv and rail uv

bbp_ng/UTIL_icons_manager.py

@@ -0,0 +1,7 @@
+import bpy
+import os, enum
+
+class BlenderPresetIcons(enum.Enum):
+    Info = 'INFO'
+    Warning = 'ERROR'
+    Error = 'CANCEL'