Add new access methods in DSL parser

 * Access to new task properties:
   input, onSuccess, OnError; any task property
 * 'dependsOn' is renamed to 'requires' and returns dict object
   which contains conditions of task transition.

  DSL can be defined either:
     task3:
       requires: [task1, task2]
   or:
     task3:
       requires:
         task1: condition1  (or empty)
         task2: condition2  (or empty)

Change-Id: Ic3ab5754443100e101f04260d9054b0a604fcd6d