Phase out opening_hours:covid19 field (#401)

…by making the field an optional field which is not displayed by default when selecting a preset. This approach allows mapeprs to easily see now potentially outdated pandemic opening hours and check/update/fix/convert them accordinly.

data/presets/craft.json

@@ -7,7 +7,6 @@
         "address",
         "building_area",
         "opening_hours",
-        "opening_hours/covid19",
         "phone",
         "website"
     ],
@@ -23,6 +22,7 @@
         "internet_access/fee",
         "internet_access/ssid",
         "level",
+        "opening_hours/covid19",
         "product",
         "ref/vatin",
         "wheelchair"