mki18n.py: generate messages.po (contains English strings in msgstr)

This po file is necessary because Transifex translation platform
automatically can only import PO files. Usually messages.pot is
enough.

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