All code that was configuring translations and style for application was
moved to Application class constructor.

The Application class constructor now loads at once all translation
files available for the current language including language file for
plugins.
Removed the translation installing from within plugin loading method at
PluginsConfigWidget.
Removed the method PgModelerPlugin::getPluginTranslator since all
plugins translation are now loaded by Application class.
Removed the method PgModelerPlugin::getPluginTranslator since all
plugins translation are now loaded by Application class.
Merge branch 'i18n-loading-change' of https://github.com/pgmodeler/pgmodeler into i18n-loading-change
Fixed some warnings triggered by clang compiler.

Fixed a crash when loading plugins on MacOSX (issue #355)
Merge branch 'i18n-loading-change' into develop