Sections and dependencies referred to as children

Embedded children 'displayed' property should be set to true once the parent has been displayed. pipeline._getTask should store new task objects in this.tasks.

Dependencies and sections are now only referred as children in specs; children that are dependencies must specify 'block' as true. Children tasks can be defined statically in the configuration or dynamically during runtime; this makes two things possible which weren't before: sections can be defined during runtime, including within non-section tasks, and children dependencies can be defined in the static configuration. The order of Pipeline flushing to the client is now guaranteed to occur in the same order that initiated the flushing; this fixed a bug where the second flush was executed before the first flush because the first flush was waiting on the frame to finish rendering, resulting in the frame appearing twice. Updated tests and sample application.