fix NPE, handle CancellationException in BitmapTileLayer
use SimpleWorker to update PathLayer
refactor and cleanup RenderElement and related classes
use depth clipping again but only when proxy tiles are drawn
cleanup TileRenderer
remove depth-projection from viewproj for tile rendering, again

- fixes issue with flickering when proxy tiles are drawn,
  where the depth buffer is used to remember previous
  clipping areas
change parameter order to be more consistent
pass non-inverted scale to TextureRenderer
Merge branch 'render_refactor'
load mapsforge germany on low zoom-level...
cleanups
reduce default in-memory tile cache size
android example: use StamenToner bitmaps
TileGridLayer