Also merge translations from $domain-content.pot

Also sync translations from $domain-content.pot. This gives us an additional entry-point for automatically created *.pot files that are not created with i18ndude. Probably we could append them to the normal $domain.pot file, but for now it seems safer to keep the two files apart.

In the future might write a buildout recipe that extracts ``ftw.inflator`` initial content translations to $domain-content.pot and add its configuration to ``plone-development.cfg``.
objections?