Force to top should support *specific* ordering

[jannisborn]

Currently when "force to top" is being used with multiple packages, then it forces all of them to the top but unfortunately does so in an alphabetical manner.

When setting:

force_to_top = ["torch", "tensorflow"]

The result will be:

import tensorflow
import torch

whereas it should be:

import torch
import tensorflow

Currently, it seems that isort does not support the ability to set multiple imports at the top of a section with a user-specified ordering. This is prohibitive because, unfortunately, some python packages have strict order import requirements.

I hope that I'm missing something! Any idea on how to solve this with isort would be much appreciated!