Modify the Essentials 'setup defaults' page.

When you start Essentials for the first time you are confronted with a 'Setup' page. This page needs modification:
1. The texts on the page need to be changed (see https://docs.google.com/a/1hippo.com/document/d/1tcoWW4PKupnpZqgrUNl_rcueBxZZiHEpnXiajLWKxy0/edit#heading=h.pgl6ye5sif28 ) for exact texts.
2. The button '+ Add repository URL' needs to be removed for the moment. Reasoning for this is that at this moment we do not want people to start to create their own versions of Essentials. A mechanism for this will be available in a next release.