Change payload from backend to frontend to be separated

[Christian-QA]

The former plan was to have the backend retrieve all data from a specific user and shove it all into one sorted case class, which is then deserialised again as it's requested by the frontend.

How it is now:
User(username, email, etc., MacroStats(stuff), Previous Weights(stuff))

This undermines the value of the backend while making the frontend unnecessarily more complex, as now the frontend has to go through the trouble of extracting individual element of the payload. The frontend also has to handle all user details for each request, rather than more specific details i.e. just Previous Weights.

A more ideal way would be to have the backend extract data into multiple case classes, each requested by the frontend separately.

For example:
User(username, email, etc.)
MacroStats(stuff)
PreviousWeights(stuff)