Focus project on a single or a set of labels

[flacombe]

Following #349, new ideas come relevant regarding labels.

As labels are intended to complete filtering ability from Osmium, I find interesting to focus a given project on a single or a set of labels. We would set this information in the project configuration and the dashboard, editors an anything on the website would be focus on defined labels.

For an example with the police project:

• Osmium filter: nwr/amenity=police
• 3 labels define gendarmerie, police_nat, police_mun
• Focus set on label gendarmerie

Then the website would only show counts, mappers, editors about gendarmerie features. Here it's obvious and we would better to filter for gendarmerie in Osmium directly. But what if we come to a filter Osmium doesn't support?

It's low priority but relevant if someone has some time to work on it.