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/modeleditor/modeleditor_plugin.cpp

@@ -43,8 +43,6 @@
 #include <coreplugin/icore.h>
 #include <coreplugin/jsexpander.h>
 
-#include <utils/mimetypes/mimedatabase.h>
-
 #include <QAction>
 #include <QApplication>
 #include <QMessageBox>
@@ -89,8 +87,6 @@ bool ModelEditorPlugin::initialize(const QStringList &arguments, QString *errorS
     Q_UNUSED(arguments);
     Q_UNUSED(errorString);
 
-    Utils::MimeDatabase::addMimeTypes(QStringLiteral(":/modeleditor/modeleditor.mimetypes.xml"));
-
     d->modelsManager = new ModelsManager(this);
     addAutoReleasedObject(d->modelsManager);