Fix codesig compatibility of GettextTools.bundle.

Xcode has issues with signing plugins/bundles that don't actually have a
binary in them.  To work around this limitation, create a tiny dummy
plugin binary with a dummy function in it.
Fix creation of plural text ctrls for new files.

Recreate the controls after the user picks the new file's language.
Use en plurals for new files with unknown language.

If the user refuses to pick the language, fall back to using English
plurals (i.e. two forms).
Merge branch 'stable' of github.com:vslavik/poedit into stable