Add pot template, update po files (missing strings)

Hi,

when preparing the extension to package for Debian [1] I noticed that there are some strings missing in the locale files.
Here's the merge request:

So I did the following:
-> generated a pot-file (po template, using  xgettext --language JavaScript -o locale/hidetopbar.pot prefs.js)
-> manually fixed the po-files, as for some language xgettext got it wrong (wrong fuzzy translation)
-> translated the two new strings into German. (Please review, as I am not sure about how to translate "pressure barrier" (I used "Druckempfindlichkeit" as I thing this gets it best)

Best regards,
coldtobi

[1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=735222