hub and spoke metaphor

[mhagdorn]

closes #79

This PR is based on top of #78, so this should get merged first. changes are mostly in module 1

[dokempf]

Note from meeting: Magnus will remove the "central" terminology introduced in favor of "Hub" and add a paragraph explaining "Embedded RSE" in the Intro. After that, it is ready to be merged.

[mhagdorn]

Note from meeting: Magnus will remove the "central" terminology introduced in favor of "Hub" and add a paragraph explaining "Embedded RSE" in the Intro. After that, it is ready to be merged.

@dokempf, central RSE team is used throughout the paper. That's a bigger tidying up job. We could clarify in the intro "RSE Hub" by adding something like

We use central RSE unit interchangeably with RSE hub even though for large federated research organisations there might be a complex arrangement such as a network of RSE hubs.