Compassion projects

Adds German translation to child descriptions.
Adds Project information retrieval.
If I remember right, this is a trick to get the name of the city translated. If I'm right, and if you also agree to this strategy, a comment would obviously be welcome!

I didn't define clearly the way to manage such cases. The point to think about would be:
- should we rename compassion_child_property_value to something more appropriated? (Translated value)
- should we keep this many2many relation even for many2one relation?