[#8] Change border color when clicking on region
[#8] The activeFeatures is just an array, not an Object

We don't need a key/value pair. The key is the same for all (resourceKeyField),
we're just adding values.

This might make it slower, because we have to search in an unordered array
every time someone clicks on a region (O(n) complexity), against simply
checking the existence of a key in an Object (O(1) complexity). But, as there
probably won't be many active filters at once, it shouldn't make much
difference.
[#8] Change URL filters when activating regions
[#8] Activate geojson's features when loading the map with filters already set

I tried isolating this routing/activating logic as much as I could. Actually,
they should be in a separate file, with most parts being reused between all
resource views that understand those filters, but we're not there yet.

The name "router" is a bit misleading, as it's not only routing, but styling
the features, but I couldn't think of anything better.
[#8] Fix bug where we were unable to remove filters

The problem was that we were concatenating the active filters with whatever was
already in the URL. This is wrong: we should simply use the active features,
overwritting the URL.

This will work fine, because when we load the page we already put the filters
from the URL into our activeFeatures hash.
[#8] Rename .activate to .toggleActivate, which makes more sense
[#8] Change styling of active features to make them more proeminent