Workflow fixes around completing tasks and added task type property

Had to completely re-write the handling of task updates for the public API as it did not support variables (the variables passed to completeTask were not passed through either). Eliminated extra data being sent in the legacy API implementation.

Removed any workflow specific knowledge from the SDK.

Changed the "properties" parameter to "variables" on completeTask for consistency.

Added a type parameter to AlfrescoWorkflowTask so the UI can reliably detect when to show correct set of transition buttons.