OS X|qmake|libgui: Various tweaks for better OS X 10.10 compatibility

The assumptions are that Qt 5 is being used and DisplayMode is disabled
so that the OS X fullscreen mode works properly.
Cleanup|Renderer: Bloom shader definition
OS X: Support HiDPI display resolutions

This commit makes Doomsday aware of HiDPI display resolutions on OS X.
DisplayMode.DPI_FACTOR can be checked to see what is the current
device pixel ratio (2 for HiDPI, otherwise 1).

Tweaked various widgets in libappfw so that hardcoded pixel sizes are
scaled to device pixels as appropriate.

Canvas was updated to translate mouse coordinates to device pixels.

The default UI style applies DisplayMode.DPI_FACTOR for rules, fonts,
and images.
Default Style: Typo
OS X|Shell|GUI: HiDPI compatible drawing of the log history

The text canvas is drawn in an offscreen buffer, so the scaling must
be manually handled.
Fixed|Shell|Qt: Thickness of lines in map overview (with Qt 5)

The default pen behavior in Qt 5 has been changed so that any
transformations affect the pen width.
OS X|Shell|GUI: Shell's About dialog uses the 2x image with HiDPI
Fixed|Updater|UI: Apply HiDPI scaling in download progress indicator

This ideally should use a Rule, though.
Merge branch 'osx-yosemite' of ssh://github.com/skyjake/Doomsday-Engine into packageloader