Fixed bugs and enhanced Mingle plugin

Mingle: refactor alm_update_task_status() to remove duplicate code
https://www.pivotaltracker.com/story/show/58027632

Mingle: Prevent content syncing when 'anonymous_accessible' is true
https://www.pivotaltracker.com/story/show/58925382

Validate custom Mingle configs
https://www.pivotaltracker.com/story/show/58667400