Feat: Removed deformations outside the body in the 'warp' files.

[LalithShiyam]

The spit out warp files (both forward and inverse) contain deformation fields outside the body. This might be due to the scatter. It would be wise to use a body mask to remove the deformations outside the body.

• Lift of the nifty masker script from enhance-pet repo
• Write a function to mask the body from the warps