[immodule-qt] introduce description() function

[Kazuki Ohta]

Hi, all.

I've committed the code on r49 to use displanName() on QPopupMenu in 
QMultiInputContext (thanks Yamaken).

Now I consider we should introduce the description() function as well as 
displanName().
This aims to show the description of InputMethod as a whatsthis (@see 
QPopupMenu->setWhatsThis(int id, const QString &text) ).

How about?

regards.

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Move the worl:D!
Kazuki Ohta : mover at hct.zaq.ne.jp