introduce neurodocker based generation of images

[PeerHerholz]

This PR introduces the first draft for a potential neurodocker based virtualization of rsHRF. It adds the following files:

• generate_rshrf_images.sh: a bash script/function to create Docker/Singularity files based on neurodocker and, if indicated, build them locally
• Singularity: the Singularity created through generate_rshrf_images.sh

Changes were made to the following files:

• Dockerfile: the Dockerfile created through generate_rshrf_images.sh

Things that need further discussion:

• change from alpine to neurodebian base: @madhur-tandon could you maybe help here?
• once merged, a potential support for binder could be integrated

[madhur-tandon]

Hi @PeerHerholz Thank you for the PR! I am not sure as to what help / discussion is required. About the alpine base, I only used it since it's very lightweight. Using alpine allowed us to reduce the image size from 3 GB to around 207 MB and to just 69 MB after compression. However, feel free to change the base! As long as it's linux based, there shouldn't be any problem. Since the neurodebian base is also derived from the ubuntu base I guess, there shouldn't be any problem indeed. Have you tested the new docker / singularity images though?