instant_answer: use focus when a region is specified

[remi-dupre]

Use a region code in the params to trigger use of the focus in instant answers.

For example when looking for "Ikea la vallette" from france:

# We get results from Germany by default
$ curl "http://localhost:5000/v1/instant_answer?q=ikea%20la%20valette&lang=fr" | grep "Am Wandersmann 2-4 (Hofheim am Taunus)" | wc -l
1
# We get results from France with the region set
$ curl "http://localhost:5000/v1/instant_answer?q=ikea%20la%20valette&lang=fr&user_region=fr" | grep "zac Valgora, 83160 LA VALETTE DU VAR" | wc -l
1

This still requires:

• stabilization of the parameter name
• a few tests, there is actually two distinct mechanisms using the focus (for intentions and no intentions)

I used the region database from erdapfel and removed fields that are not likely to be used. I kept bbox as it may be useful in the future if we want to tweak the zoom level depending on the region size (a purely naive approach would not fit, for example France's bbox covers most of the world).

[remi-dupre]

@amatissart I've just rebased and pushed