add Simon Z and Jan G (Holisticon) to contributors page

Hi

as discussed with Bernd, I added Simons and my profiles to the team/contributors site and also added the holisticon  logo to the partner column.
Simon and I are currently setting up "Camunda-bpm-testing", the one place where all testing tools and methods are combined, based on the plexiti contribution "fluent-assertions" and BDD/jbehave.

We will give a little inside on this in our innovation talk at the BPMCon on friday.

see you there

Jan