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.

[TOPOLOGY]
NetName=None
Nodes=0x01
Node64Present=0x01
Node64Name=micromod
Node64DCFName=PEAK MicroMod.eds
EDSBaseName=eds