Using hardcoded names to retrieve modifiers can result in errors if
the user has enabled UI translation, because the new modifiers may not
have the expected English names if the UI is translated.
So, use the data API to create the modifiers instead of the ops API,
and assign nodes to variables instead of getting them by name.
This should take care of most of the class property conversions to
use the new annotation format (colon instead of equals) for
assignment. There may still be a few edge cases that were missed.
Bumped version to 2.4.2
Pep8 cleanup
Moved scene properties to a property group
access it through context.scene.auto_mirror
remove the properties upon unregister
Add poll checks for Mesh objects to operators
Add missing operator description
Remove the draw function from the AutoMirror operator
since it is not used and enabling Undo will not work
in this case, since depending on the initial settings
it can produce unwanted results
