Move mimetype definitions to plugin specs

- Avoids the hassle of QRC files and manually registering mime types
- Avoids performance regressions because of mime types that are
  registered after mime database has been used
- Makes it technically possible to detect that a disabled plugin could
  handle a mime type if it was enabled

Change-Id: I373008b1b56e9c6b4853055f20b3eeb112a6eff9
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/scxmleditor/scxmleditorplugin.cpp

@@ -36,7 +36,6 @@
 #include <QMainWindow>
 #include <QMenu>
 #include <QMessageBox>
-#include <utils/mimetypes/mimedatabase.h>
 
 #include <QtPlugin>
 
@@ -52,7 +51,6 @@ bool ScxmlEditorPlugin::initialize(const QStringList &arguments, QString *errorS
     Q_UNUSED(arguments)
     Q_UNUSED(errorString)
 
-    Utils::MimeDatabase::addMimeTypes(":/scxmleditor/ScxmlEditor.mimetypes.xml");
     addAutoReleasedObject(new ScxmlEditorFactory);
 
     return true;