Create task to reprocess failed documents

[DavidLemayian]

Apart from reprocessing the last failed document from the admin console, we should be able to do it from the console as a task. This can be defined as:

rake production app:reprocess_failed

Possible options could include (exclusively):

1. Process all failed docs when no arguments passed.
2. Document id argument
3. Organisation id argument
4. Account id argument
5. Last failed flag