i18nbuild: Remove "Domain", "Language-Code" and "Language-Name" headers.

Plone does not need those headers, it takes informations from the path.
The headers are usually not set correctly, so we just remove them.
Add hint about header removal behavior to readme.
Merge pull request #2 from 4teamwork/jone-i18nbuild-remove-unnecessary-headers

i18nbuild: Remove "Domain", "Language-Code" and "Language-Name" headers.