Add available workflows by category

When some datasets we would need to retrieve from ewoks server the set of available workflows

This is done via http://ewoksserver1.esrf.fr:5000/workflows/descriptions

The list of workflows could be displayed in the selection page:

And once the workflow is chosen, we need to retrieve the tasks: http://ewoksserver1.esrf.fr:5000/workflow/mx_test_workflow

And then get the parameters: http://ewoksserver1.esrf.fr:5000/task/MxTestTask