This reverts commit 1368ec36.

Stas Boukarev authored Sep 20, 2016 and Friedrich W. H. Kossebau committed Sep 20, 2016

Summary: Use devicePixelRatio to properly scale cached pixmaps on HiDPI screens.

Reviewers: nienhueser, #marble, rahn

Reviewed By: nienhueser, #marble, rahn

Subscribers: kossebau

Differential Revision: https://phabricator.kde.org/D2152

- clipper library seems more robust (less clipping glitches, no
  endless loops) at this point, but might switch back later
- clipper library (version 6.4, Boost license) C++ code inside
- VectorClipper::clipTo() has an internal switch to select between
  BaseClipper and clipper library

Since we display tile level n up to zoom level n+1, reduce nodes
for level n+1, not n.

- fixes water background color for lower level tiles
- at the same time breaks background color for medium and high
  level tiles on landmass that don't have their own background areas,
  but this will be fixed soon with proper landmass backdrops
- darker bathymetry 200 / 4000 fill color to distinguish them from
  plain water

Improves rendering of Berlin TV tower a bit, makes building of Volksbühne (https://www.openstreetmap.org/relation/5746885) appear.

Buildings are taken care for already by osmVisualCategory().

An external browser greatly enhances browsing experience:
* no more too small window
* tabbed browsing
* save web pages, add bookmarks
* more privacy (adblockers)
* browser extensions