File discovery: also include the base directory

This is a regression introduced in e834585 which prevented Pootle's
terminology feature from working properly when the app was deployed using
a git clone.
Cleanup: Remove unused code
Random cleanups
Cleanup: Move function inside factory

It is not used in any other place and this simplifies code making it
more readable.
Cleanup: Just close and reopen files once
Cleanup: Remove unused code in ODF conversion

Appending the translated XLIFF file to the translated ODF file is not done,
probably because it complicates testing the roundtrip conversion.