integrating leanpub changes
merge
Complete translation
German simple form translation
from leanpub
Merge branch 'german' of https://github.com/NeQuissimus/leanpub_localization
fixed language key typo thanks to Tim
merging back fixes from leanpub
merge from leanpub
Fixed Dutch translations

I noticed some missing translation on the site, and found this github repo. 
The Dutch translations in here seem to be Google translate generated, so I've
tried to fix them up. Made use of 'u'/'je' consistent. Made use of 
kredietkaart/creditcard consistent. I've leaned towards using 
modern/borrowed-english versions of words, as some of the used 'real' Dutch 
words seem archaic.
Fixed Dutch translations

Fixed auto-translated Dutch file
merge leanpub
from leanpub