[REG 3.3 -> 3.4] MimeDatabase: QML files being opened in CPP editor

1. Create a new Qt Quick Application project.
2. Open the QML file from the project.
   It's being opened in a QmlJSEditor::Internal::QmlJSEditorWidget. Highlighting works correctly.
3. Open tests/manual/qml/testfiles_quick2/helloworld.qml from Creator's repository.
   It's being opened in a CppEditor::Internal::CppEditorWidget. Highlighting does not work.

QML files should always be opened in a QML editor.

Found and tested by Squish test tst_delete_externally and others.

Introduced by self-reviewed commit:

5a3a940ad3b3984b308b539e7f0456ce11d4d90e is the first bad commit
commit 5a3a940ad3b3984b308b539e7f0456ce11d4d90e
Author: Eike Ziller <eike.ziller@theqtcompany.com>
Date:   Wed Feb 4 09:32:46 2015 +0100

    Use new mime database
    
    Change-Id: I4305872b6b11ef3e8a364280ffa5209a5a793600
    Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>