Fix on Python object DatabaseObjectSelector

[rodrigoramosrx2]

Fix to DatabaseObjectSelector, because the buttons "add" and "remove" doesn't working.

[mysql-oca-bot]

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[rodrigoramosrx2]

Ok I just signed the OCA.

[mysql-oca-bot]

Hi, thank you for your contribution. Please confirm this code is submitted under the terms of the OCA (Oracle's Contribution Agreement) you have previously signed by cutting and pasting the following text as a comment:
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[rodrigoramosrx2]

I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

[mysql-oca-bot]

Hi, thank you for your contribution. Your code has been assigned to an internal queue. Please follow
bug http://bugs.mysql.com/bug.php?id=113725 for updates.
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