Improve Japanese translation of "Open".

Some of translation of "Open" is translated as オープン in QT resources.

<message>
<source>&Open</source>
<translation>オープン(&O)</translation>
</message>
<message>
<source>&Save</source>
<translation>保存(&S)</translation>
</message>

Above resource is used for Open button. It should be translated as 開く, otherwise, translation cannot be consistent in eitehr Windows or Mac O/S resource translation style.