Use level:ref in place of level when showing levels for items where possible

[tazz4843]

See https://wiki.openstreetmap.org/wiki/Key:level:ref

Level:ref is a property that specifies the ref or name of the level where an object is located, using the locally common method of indicating a specific floor. Particularly useful where levels are not referred to by numbers but by codes (level:ref=A) or by names.

This also solves the problem of building numbering being different than the level key (ie here there's a building for which the bare level key is offset from what the actual signage shows, while level:ref across the building shows what's on signage).

See also: organicmaps/organicmaps#4452 (comment)