PennAI image for raspberrypi

I pushed a branch called [raspberrypi](https://github.com/EpistasisLab/pennai/tree/raspberrypi) for trying building docker images of PennAI in raspberrypi.

This issue is for discussion of solution for transporting PennAI based on x86 (most Intel and AMD CPU) to ARM (raspberrypi's CPU and Apple M1)

Below are things I have tested:

- A 64bit Linux OS, like [Raspberry Pi OS (64 bit) beta test version](https://www.raspberrypi.org/forums/viewtopic.php?f=117&t=275370) is needed for installation of dbmongo docker images.
- Docker and docker-compose can be installed in the Raspberry Pi OS (64 bit) beta test version (see this [instruction](https://dev.to/rohansawant/installing-docker-and-docker-compose-on-the-raspberry-pi-in-5-simple-steps-3mgl))
- dbmongo docker image can be built with the commit 7ad961ede379e59118c2ee950635a191d69a3fba
- python and node can be installed into lab docker image with the commit c8e51b39db5621bef478d4b7ba36439b8714053c

But some python packages (like numpy and pandas) were failed to installed due to ARM6 architecture, we may find a way to re-complile them from source codes.