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
