Resolve "Proxy submission"

Links to relevant issues

Description of changes, providing context that may help others understand the changes

This feature allows to add submissions in the name of another user:

• browse and open a survey with an admin-user
• press the new dropdown option of the button "Start survey" and choose "Start survey as a member"
• choose a member
• enter survey data
• the selected user is named in the survey summary, on the submit button and in the confirm dialog
• the submission data is enriched by the following information: - creator: the user id of the selected member - creatorDetail: email and name of the selected member - proxyUserId: the user id of the proxy user who actually submitted the data - proxyUserDetail: the user email and name of the proxy user

Technical hints:

• in the scope of a submission draft, all requests to the backend contain a header param called delegateToUserId which can be used by the service controllers
• currently, the service endpoints get /farmos/assets and post /submissions do use the header value of delegateToUserId to overwrite the caller's user._id
• in addition, the endpoint post /submissions backups the actual caller's user._id in a value called res.locals.auth.delegateByUserId, which is then stored in the submissions meta data to allow backtracing of the actual caller

Closes #126 (closed)