Slicer modifies Slicer.tasks

[sagarjauhari]

Based on the current design, after some of the methods, slicer modifies the tasks, for e.x.:

https://github.com/sagarjauhari/eeg_mining/blob/pipeline/slicer.py#L65

Because of this, if slicer object is passed and some other method needs to be called, we need to reload the tasks first and then call another method which uses the original loaded tasks. It'll be good if slicer keeps the original tasks in native form and creates temporary modified tasks when required.