improve batch-wise grasp generation in sampling scripts

[kuldeepbrd1]

To resolve issue #4

• added consistent use of batch_size and device variables
• added sampling loop to support desired n_grasps
• added device and batch_size as cli args
• Auto-sorted imports and format changes from black

[kuldeepbrd1]

@TheCamusean

In the diff for the changed files, you will also see that there are lots of formatting changes (indentation, terminal spaces, linebreaks etc). These were automatically included in the commit as I use auto-format on save using black. I only noticed later.

Let me know if you want me to remove these auto-formatting changes. Happy to also do that :)