Add support for OpenType (.otf) fonts

FreeType already has support for the file format, so simply
ensure they are picked up by the generic database. (Other backends, 
such as Windows, already had support)

[ChangeLog][QtGui] Qt's generic font database now adds OpenType fonts (.otf).

Change-Id: Ief5a3329e66b8066aad284172afd004f2cdfaebb
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

src/platformsupport/fontdatabases/basic/qbasicfontdatabase.cpp

@@ -103,7 +103,8 @@ void QBasicFontDatabase::populateFontDatabase()
     QDir dir(fontpath);
     dir.setNameFilters(QStringList() << QLatin1String("*.ttf")
                        << QLatin1String("*.ttc") << QLatin1String("*.pfa")
-                       << QLatin1String("*.pfb"));
+                       << QLatin1String("*.pfb")
+                       << QLatin1String("*.otf"));
     dir.refresh();
     for (int i = 0; i < int(dir.count()); ++i) {
         const QByteArray file = QFile::encodeName(dir.absoluteFilePath(dir[i]));