Add the possibility to create combined filters

[afonic]

A "combined" filter would be searching at more than one field at a time. For example let's say we have a field that's called "Brand" and contains the car brand and a "Model" field that has the model.

Now these need to be different filters, but ideally we would like the user to search for car name in one field and get results if he inputs either a brand or the model.