Step-by-step mode vs autonomous mode

[mondaychen]

Add an option so the user can have the option to confirm each step before executing. It feels safer to user especially for tasks that are not reversible (placing order, deleting item, etc.) During task execution, user can "stop" a task which terminates the current task. We should support "pause" so that user can pause the current task execution after it performs an action, and can then resume. This will make #91 easier to do too.

Need to confirm on UI design before proceeding.