Refined translations for German

- Removed superficial "Mit" preposition
% Correcte the OpenStreetMap link
% Replaced &UUml; with Ü (umlauts)
Update de.l20n

Removed unused strings
Update ast.l20n
Update en.l20n
Update es.l20n
Update fr.l20n
Update ja.l20n
Re-Adding the necessary strings
Merge pull request #11 from guerda/master

i18n : refined translations for German and removed all the strings not needed anymore.