* Added state transition support to generic states
* make can_cancel a property everywhere
* add check if method is defined
* add unit tests
* extend tests
* fixed loading of broken classes
* added test to ensure transition functions are called
* added cleaning step for custom classes
* change description texts
* added state transitions to SalesOrder, ReturnOrder
* renamed internal functions
* reduced diff
* fix keyword def
* added return funcion
* fixed test assertation
* replace counting with direct asserting
* also pass kwargs
* added sample for transition plugin
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