Scatterd

* Remove warning when fontsize is set to 0

* Logging is standardized and replaced by print messages.
* The standardized verbose setting are: `60 or 'silent' , 40 or 'error', 30 or 'warning' , 20 or 'info', 10 or 'debug'`
* The library datazets is used to import example datasets and the libraries request and wget are removed.
* Docstrings updated

* Add new function to init: jitter_func, normalize_between_0_and_1
* update jitter function and code cleaning

* Added parameter to set different method for the opaque `opaque_type`: `per_class, all and lineair`

* fix for import

* Density in figure is improved. The default is set to `gradient='opaque'` which will automatically include transparency of points based on the density of the data.
* bugfix for `zorder` when it was None