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.

          <xsd:attribute name="Command" type="xsd:string" use="optional" default="make -C %(buildpath)s all BEREMIZSRC=%(src)s BEREMIZCFLAGS=%(cflags)s MD5=%(md5)s USE_BEREMIZ=1 FROM_BEREMIZ=1"/>