Palettes menu entry not translatable

Discovered by watery on IRC.

It seems that all that would be needed is to add the text from the line above to https://github.com/musescore/MuseScore/blob/master/mscore/shortcut.cpp#…

Text is currently set to the _desc property, but not to the _text property, which would be the one to use for it to show up on buttons/menus according to the code comments.