Adding shop symbol: hearing_aids (#4909)

* Adding shop symbol: hearing_aids

Icon source: own work.
Rasterisation: tested with density=96,150,300,600 using ImageMagick convert

* improves rendering of hearing_aids icon

Using: kosmtik, mapnik
Visual change: a) thicker and longer icon to better resemble the human ear; b) improves pixel grid alignment and simplicity

* Improving hearing_aid symbol due to preliminary discussion

This version is based on number 28, with minor improvements and
svg optimisations (number 43). This symbol depicts the human ear
with an over-the-ear hearing aid being visually slightly separated
from the ear, as well as with sound waves propagating from behind
towards the hearing aid receiver.

Attention was given to a) uniqueness, b) visual simplicity, c)
rendering quality using kosmtik as well as png export with multiple
scaling factors (1x and 2x).

project.mml

@@ -1672,7 +1672,7 @@ Layer:
                                 'laundry', 'dry_cleaning', 'beverages', 'perfumery', 'cosmetics', 'variety_store', 'wine', 'outdoor',
                                 'copyshop', 'sports', 'deli', 'tobacco', 'art', 'tea', 'coffee', 'tyres', 'pastry', 'chocolate',
                                 'music', 'medical_supply', 'dairy', 'video_games', 'houseware', 'ticket', 'charity', 'second_hand',
-                                'interior_decoration', 'video', 'paint', 'massage', 'trade', 'wholesale') THEN shop
+                                'interior_decoration', 'video', 'paint', 'massage', 'trade', 'wholesale', 'hearing_aids') THEN shop
                                 ELSE 'other' END AS shop,
               CASE WHEN building = 'no' OR building IS NULL THEN 'no' ELSE 'yes' END AS is_building,
               tags->'operator' AS operator,

style/amenity-points.mss

@@ -1090,6 +1090,10 @@
       marker-file: url('symbols/shop/optician.svg');
     }
 
+    [shop = 'hearing_aids'][zoom >= 18] {
+      marker-file: url('symbols/shop/hearing_aids.svg');
+    }
+
     [shop = 'outdoor'][zoom >= 18] {
       marker-file: url('symbols/shop/outdoor.svg');
     }