FR: Ranged attribute selection via min/max filter

[dougy83]

For attributes having a range of value, e.g.

It can be a bit of work to select e.g. all parts with a maximum input voltage >= 40V, as you'd need to select {"2.5V~40V", "5V~40V", "16V~44V", "16V~65V", etc.}

Items might be more easily selected if ranged attributes could be filtered by a max-lower-value and a min-upper-value, which would allow selecting the matching attribute values from the multiselect box. For the example above, this would just require setting min-upper-value = 40

This change can be front-end-only, as ranges can generally be detected by their format.

[dougy83]

Implemented in #127