[selectors] modify workflow selectors: is_in_state, on_transition - factorize `is_on_state` selector - add new `on_transition` selector Especially useful to match pending transitions to enable notifications when your workflow allows several transition to the same states. Note that if workflow `change_state` adapter method is used, this selector will not be triggered. In debug mode: These both selectors will check against the entity current workflow if expected values given in selector argument are valid. ValueError exception will be raised for unmatching state/transition names against the current workflow (generic etype workflow). (check against custom workflow is not implemented)

addressbook
basket
blog
book
calendar
comment
company
email
file
folder
i18ncontent
keyword
link
mailinglist
person
tag
timeseries
vcsfile