Expand the methods available in the stored_progress_bar output component
and stored_progress_task_trait to allow a progress bar to be created in
a "pending" state before the associated task is executed.
- Alters existing progress_bar class to support extension
- Adds stored_progress_bar class as child of progress_bar
- Adds webservice to poll stored progress
- Updates database tables
- Bumps version
- Adds unit/behat tests