More rebranding

Closes: #39

Mostly done with rebranding now. We just need to translate some services
to PolyMC.

launcher/ui/pages/instance/VersionPage.cpp

@@ -395,7 +395,7 @@ void VersionPage::on_actionDownload_All_triggered()
     {
         CustomMessageBox::selectable(
             this, tr("Error"),
-            tr("MultiMC cannot download Minecraft or update instances unless you have at least "
+            tr("PolyMC cannot download Minecraft or update instances unless you have at least "
                "one account added.\nPlease add your Mojang or Minecraft account."),
             QMessageBox::Warning)->show();
         return;
@@ -635,4 +635,3 @@ void VersionPage::onFilterTextChanged(const QString &newContents)
 }
 
 #include "VersionPage.moc"
-