Renaming of tasks and subtasks

[s-ramaswamy]

Tasks should be renamed to Objective/Motive/Aim/Goal and Subtasks should be renamed to tasks. The current hierarchy is rather confusing

[s-ramaswamy]

Don't work on this. This is on hold.

[akshayrangasai]

@meetaw Update this issue now.

[s-ramaswamy]

I thought @BademiChetan wanted a abstract task model that eliminates the need for a subtask model ?