Allow point range input

Aim

Range field has a formatter setting for point ranges, i.e. ranges wher "to" = "from".
It should also allow to input it in an intuitive way similar to this:
* Selector "value" or "range" (where "value" stands for a point range)
* If "range": "from" and "to" widgets
* If "value": "value" widget

A point range will be stored as from = to = value (which is essential for subsequent comparison operations).