Data object not updated with sequential read then write

[alongreyber]

When calling:

PUT /api/:id/data
then
GET /api/:id/data

in quick succession, the data is not available. Likely cause is that the Go server is multithreaded by default, so the GET request is processed before the PUT finishes writing the file. We will need to write a test to confirm, and then fix probably with an RWMutex.