improve installation, support remote usage

[dashidhy]

Hello kuixu. Thanks for your great work! I met some installation problems when I began using your code and I tried to use the code remotely on a GPU server without GUI support but always failed. These problems were not quiet easy to solve due to complex dependencies of mayavi, but after spent some days on them I finally made it. So here is this PR.

What included:

• Isolate the installation into a new conda environment to avoid conflicts, use more official pip installation of opencv, use conda-forge to manage mayavi dependencies
• A step-by-step tutorial and some notebook demos of remote usage that using Jupyter Notebook to substitute local GUI, which benefits researchers who heavily work on a remote server
• remove some unused variables and fix some small bugs

Hope this can help more people.

[kuixu]

That's pretty cool! Thank you so much.