Write microservices with docker image

[Siemienik]

The proposition is to write a microservice for xlsx render and xlsx-import.
It will be a small nodejs app + docker file, and docker image with the current version.

[Siemienik]

I am curious about it, Imo it will be a significant change. For now, I marked it as a proposal. Will be accepted soon.
Added into The Proposals Index (#144).