Iss 828 Fieldwork section rework

[alex-cit]

WIP #828
Structure of the Fieldwork section updated

• the content is just roughly sorted out to see how it would look like, if we agree on the structure, I will go through it in more detail
• Field Survey Setup is a new / proposed page (content not included yet)
• How to Fix a Broken Project is removed from the sidebar, it is referenced from the Support and Troubleshooting and renamed as "The Mobile App Fails to Save Changes or Fails to Read Project ".
• some mobile app content that is now in the Manage section (switching workspace, creating a project) was not moved to the Fieldwork section - as discussed, we will see how we want to structure the docs, can be moved later
• no redirects so far