Parameters hover explanations during task creation

[JulienVig]

#710 by @tomasoignons implemented great hover explanations for parameters to define when creating a new task in the webapp:

A next step would be to add more specific format requirements (e.g. are we expecting integers, a fraction between 0 and 1 excluded, etc.) as well as textual information about what the parameter is and how to find an appropriate value.