Prepare computation before it is started #10
Description
Since it can take significant time to download, extract and load a Docker image from DaRUS, the idea is to already anticipate an upcoming computation task when the frontend is started, i.e., when a computation template is rendered.
For that, a prepare-message-type has been already added in the Websocket-API and in the frontend, but integration in the backend is missing.
See discussion in #5
Relates also to VirtualProgrammingLab/viplab-websocket-api#292