Add due_date to tasks
Mark overdue tasks and sort incomplete tasks by overdue first
Add completion percentage to projects
Clean up project_completion_percent code
Add optional tags to tasks
Tags are stored in array, not hash
Projects can be searched for tasks with matching tags
Put tags in options hash to make recurring easier. Fix search method to compensate
Tasks have frequnecy based on @recurring
Recurring tasks can be repeated (copied) with repeat_tasks method
Rebuild terminal client class as an actual class
Fix add_task method in terminal to account for due_date