Resource view - mark the zoom context better

[fbarl]

Some ideas from the updated mockups:

• Add a horizontal metrics scale below the base resource layer to know what the resource box width stands for at the current zoom level.
• Do not render very thin resource boxes in have a text like + 31 more in their place - this would change dynamically as we zoom in and out.
• Consider putting a zoom scale info somewhere, sort of zoom x 3.2, perhaps as a part of solving zoom control not obvious #2321.