Colab demo requires multiple upgrades

1. Devolearn requires `torch==1.7`, but I think it would also work with the latest versions of torch. Using the latets version of torch would make the installation much faster on google colab notebooks because the latest version of torch is already installed there.
2. The URL for the weights to the embryo segmentation model is most likely broken, throws an HTTP error.
3. arg `mode = 'cpu'` should be replaced with `device = 'cpu'`
4. optionally, we can also let the user decide the GPU ID like `device = 'cuda:0'`
5. move the `run tests` cell to the bottom

Note that this is a beginner friendly issue, all the changes are to be done on [this notebook](https://colab.research.google.com/github/DevoLearn/data-science-demos/blob/master/devolearn_docs/devolearn_quickstart.ipynb). Feel free to reply to this if you're willing to take this up.