Better support for hdpi/mdpi/ldpi/tvdpi densities

[cyrilmottier]

Polaris currently contains only xhdpi resources. Technically speaking, this is not really a problem because the system automatically scales the resources to fit the display density. However, system scaling can produce blurry and inaccurate which results in a not-so-polished map.

The best solution is to create resources for all of the supported densities