Added Memory Persistence API and Generic Datatypes

Added a generic persistence API for JobBoards,
Jobs, LogBooks, Workflows, FlowDetails, Tasks,
and TaskDetails. The currently implemented
backends are in-memory. Also implemented generic
return types (listed above) for the generic API.

Change-Id: I6d09860ee08a900faf2c213a230429bf9e0dec01
Merge "Added Memory Persistence API and Generic Datatypes"