Added priority counter to ClassDecorator to resolve key clashes
Added priority counter to ClassDecorator to resolve key clashes

The priority counter ensures that a method decorated in a subclass takes
priority over a method (of the same name) decorated in a superclass. For
instance, this is important if the type of a sheet is changed in a
subclass.

mjabri/topographica,Tasignotas/topographica_mirror,Tasignotas/topographica_mirror,mjabri/topographica,mjabri/topographica,mjabri/topographica,ioam/topographica,mjabri/topographica,ioam/topographica,ioam/topographica,Tasignotas/topographica_mirror,ioam/topographica,ioam/topographica,Tasignotas/topographica_mirror,Tasignotas/topographica_mirror