offer task descriptions from server (and design task description format)

[martinjaggi]

the auxiliary server needs to be expanded to host task descriptions. each task description should contain:

• title of the task
• description string (maybe as md format)
• features description (list for tabular data, or e.g. image format description), and label description. best to include an example datapoint
• DL model architecture (TF.js model.save)
• training hyperparameters (learning rate, dropout etc)
• initial model weights (can also be used for sharing model snapshots later, or when new nodes join)

to share it with the client we could organize them also via json for example, for the machine readable variant.

once it works, convert the dummy csv task (adult dataset) and mnist (image) tasks to this format an make sure they still work

human readable format: the task description should also be easy to visualize in human readable form, in HTML (so it can be served by th server as well as locally on the client)