Optimize dockerfile

[mmartinortiz]

Hi,

I have taken a new look to the Dockerfile of the backend. I think that some things are redundant, so I tried to remove overhead writing a single Dockerfile.

This new Dockerfile:

• Separates the build in different stages
• Installs as many libraries from the official Ubuntu repository as possible
• Installs only required libraries
• Cleans up not needed software at the end
• Reduces the final build in 1.5Gb

Even though, I think that it could be optimised a bit more.

Please, test the image generated and its integration with the rest of images that composes Librephotos. I only tested the build in AMD64. I could start the service with the Docker compose but I could not setup a folder to be scanned (what I think it is a different issue)

Regards, Manuel

[derneuere]

Thanks for the --no-cache command for pip. This reduce the size alot! I close this pull request as the dockerfiles changed alot :)