Workflow decider

Notes made in Paris:

    * decide (on input), transform data. Why put in workflow? To avoid polluting action library. It's a worfklow-only, can't be reused outside of workflow?
    * idea: lua/javascript action to define arbitrary sandboxed script to do manipulation on execution context, publish/republish variables and "define outgoing branches".

So the general idea is to provide workflow DSL means in order to do more complex data transformations if needed. It may be a completely new entity in workflow, different from task but used in conjunction with tasks.