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/cpptools/cpptoolsplugin.cpp

@@ -140,8 +140,6 @@ bool CppToolsPlugin::initialize(const QStringList &arguments, QString *error)
     Q_UNUSED(arguments)
     Q_UNUSED(error)
 
-    Utils::MimeDatabase::addMimeTypes(QLatin1String(":/cpptools/CppTools.mimetypes.xml"));
-
     CppModelManager::instance()->setParent(this);
 
     m_settings = new CppToolsSettings(this); // force registration of cpp tools settings