convert FindInPouDialog from wx.Frame to wx.Dialog

In this case FindInPouDialog Windows isn't listed in windows manager
on Alt-Tab. And it's not shown on top of other applications. For
example, previously the dialog was shown even on top of web browser or
word processor.

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<Python xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.w3.org/2001/XMLSchema" xsi:schemaLocation="python_xsd.xsd">
<![CDATA[]]>
</Python>