Added Archived flag to Task object (no code utilizing it yet, but it's there).

Added migrations for Archived flag.
Modified Task Repo GetCurrentTasks to only return non-archived tasks.

Added 'ArchiveTask' method to TaskService.

Changed TaskController to archive tasks instead of deleting them when the user presses 'X'.

Cleaned up TaskRepo tests.
Fixed issue where newly added tasks were not added to current day.