WinRT: Load system fonts using DirectWrite

System-installed TrueType fonts can be read into memory and loaded into
the FreeType font engine. This allows the application to be packaged
without fonts, but does not work on Windows Phone where DirectWrite is
not supported.

Every single-file TrueType font is registered with the font database,
and then loaded into memory at the point that the font is actually used.

Task-number: QTBUG-37230
Change-Id: I804116e37a874cd146a0653ba4cc018f8b1cd6a4
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>
WinRT: Fix QDesktopServices::openUrl() for local files

The passed-in URL is expected to be a file-scheme URL to be converted to
a QString using toLocalFile(), not a relative path to be prepended with
the application directory.

Change-Id: I647f351c99f0df66ef017936585f044292c16aff
Reviewed-by: Maurice Kalinowski <maurice.kalinowski@digia.com>
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>