TODO

Testing
-------
- provide something like #assert_transition to test if FSM goes where we want
- assert_update/assert_execute, to assert which components are updated (e.g. after
  event chain)

State Machine
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- better debug-output for transitions
- make #transition_map friendly, maybe some more sophisticated DSL

Parameter
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- introduce #my_param or something similar so widgets can only access parameters really 
  addressed to them. or let #param do this per default.

Persistence
-----------
- only save id of ActiveRecords, to avoid big sessions (discuss whether this is necessary)
- provide session storage alternatives, like encoding in url or hidden field
- introduce a rake task to clear the frozen tree

Events
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- only send back the newer EventHandler content when more than one event was triggered
  and the content of an earlier EventHandler is overridden.
- provide scrambling of the event url, so users can not trigger events out of scope
- check if an EventHandler is executed in scope, meaning the triggering event was valid.

Apotobug
--------
- return exception reports as text, not HTML, for better reading in Firebug.

StatefulWidget
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- provide an ordered list of rendered child views.