use tilde operator everywhere (and updates)

I'm not bumping symfony/ixu since 1.0 ist the last implementation
that is native PHP. I would prefer bumping it but then it needs
icu-4.4 which is harldy available on enterprisey systems.
make /core/app localized and support writing

I introduce quite some api changes here. For the moment all write operations
need to specifiy an english string as the base translation string. Also the writing
of new (and untranslated) strings into mongodb still needs some optimization.