Automate construction of "former employees" list at DIAG

[keelinm]

Current practise is that when somebody leaves DIAG their member page is made inactive and they are added, manually, to the list of former employees, with a link to their linkedin page.

It seems that the second step is not always done, apparently people are missing from the former employees page (e.g. Wouter).

A better solution is to construct the former employees page automatically by going over the member pages, choosing those that are from DIAG group, not active, and taking their linkedin link from their markdown file.

Note 1: Computational Pathology page does this a bit differently - they list all former employees (automatically?) and link to their member page, but Bram did not want this (see #191), he wanted the linkedin link instead.

Note 2: Member markdown files will change slightly as Marina is working on making the cara-lab website so we will wait until changes for that are finalised before we work on this issue.