missing/incorrect param->widget mappings

[xavArtley]

Currently only a subset of the parameters for param module are mapped to a widget.
The mapping is the following:

    _mapping = {
        param.Action:         Button,
        param.Parameter:      LiteralInput,
        param.Dict:           LiteralInput,
        param.Selector:       Select,
        param.ObjectSelector: ObjectSelector,
        param.FileSelector:   FileSelector,
        param.Boolean:        Checkbox,
        param.Number:         FloatSlider,
        param.Integer:        IntSlider,
        param.Range:          RangeSlider,
        param.String:         TextInput,
        param.ListSelector:   MultiSelect,
        param.Date:           DatetimeInput,
    }

If a parameter is not mapped then it will be mapped to it's first super class found in _mapping
all params inherit from param.Parameter so the widget affected is LiteralInput

This issue is opened to discuss missing mapping, not relevant or wrong mapping.

• on gitter @philippjfr suggest mapping param.DateRange to pn.widgets.DateRangeSlider
• param.Filename is not mapped and LiteralInput lead to a bad behavior