Refactor Code for Fourier Transform Class and AudioBufferTask

[neel1998]

Actual Behaviour
Currently there are separate classes to handle different number of channels

Expected Behaviour
Create single class to handle all the channels

Would you like to work on the issue?
Yes

[neel1998]

@CloudyPadmal @mariobehling add this to Milestone 5

[neel1998]

@mariobehling can this be added to milestone so we can keep track of the issues closed during this week. Thanks

[CloudyPadmal]

Done