Linked Qt version is saved to installation, not to settings

1. Start Creator with parameter "-tcs".
   This shall give you temporary clean settings. (Is this what the acronym is for?)
2. Click "Link with Qt".
3. Select a Qt version and click "Link with Qt".
4. Click "Later".
5. Quit Creator.
6. Start Creator with parameter "-tcs".
   This should give you temporary clean settings, but it doesn't anymore. Creator is linked with Qt from step 3 because that is stored in the build/installation directory instead of in the usual settings.

Saving the linked Qt version to "share" instead of the respective settings directory seems wrong to me. It means that:

• User will still get the same linked Qt versions when using different settings.
• User will not get the linked Qt versions when using the same settings on a different build of Creator.