Merge branch 'use-qt5-qiconloader'

* use-qt5-qiconloader:
  Honors /usr/share/pixmaps when searching for icons.
  Adds xpm icon support
  Adds Qt5 QIconLoader for the Qt5 build

(cherry picked from commit b18046858e4911c58de1dbfd57e8177bdd65ae0b)
Fixes an FTBFS in the Qt4 build

Change-Id: Ic0d6448355be6c94fb36bd134fdfb36b25790c88
Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
(cherry picked from commit bd9510f926aeb7bbdb11b428ab2c26e82861be37)
Allows QIconLoader to search in multiple theme directories.

Even when QIcon::themeSearchPaths() returns a list QIconLoader doesn't
honor it. It will search for an icon in the first directory it finds (that
has the current theme).
QIcon still doesn't support a theme that is spread across several
directories. And it's a fundamental feature needed to support user
installed icons, e.g., the hicolor theme.