Adds Qt5 automatic load of self translations

loadSelfTranslation() will be called from the QCoreApplication constructor.
This way we can load the translation without requiring the application to
call it. It piles up, we can have all libraries translations self loaded
with Q_CORE_STARTUP_FUNCTION macro. It works for Qt 5.1 and later.

Sadly such a macro isn't available for Qt4.
Adds a translation loader for plugins

Plugins are different, they have a type or owner. The translations are
installed to a owner subfolder. The logic that applies to libs and apps
fails with plugins.
We search for the translations in /pluginnOwner/pluginName relative to the
base search path provided by getSearchPaths();
Ex: /usr/share/lxqt-qt5/translations/lxqt-panel/quicklaunch/
lxqt-panel is the type and quicklaunch is the plugin.