Make data/darktable.desktop translatable along with all other things that
need translation.  To translate, translators don't need to do anything
more than they have done so far, it just beomes a few more strings to
translate.
_Keywords got dropped by mistake, restore it
Update French translation.
tiff output: several fixes

- add TIFFTAG_SAMPLESPERPIXEL tag to avoid possible confusion in readers
- cast all values to their correct type as documented in
  http://www.awaresystems.be/imaging/tiff/tifftags/search.html
  this should fix BE archs as writing a uint16_t written as 32 or 64bit
  value would have always resulted in a 0 value being interpreted if
  varargs use the stack
- fix a bug where last strip was never written for 32bit
  (spotted w/ enfuse)
- factored the stripe allocation logic
- make 8/16/32 bit codepath similar enough to just differ by the used
  pointer type
- add proper error path for OOM conditions and tif opening failure

NB: enfuse still creates pure white images from dt float tiff :-(
Updated Danish translation
tiff output: tentatively fix compilation with libtiff 3.9 which lacks tmsize_t
Updated Dutch translation
Merge pull request #476 from MRIG/master

Updated Dutch translation
Merge pull request #474 from pryds/master

Updated Danish translation
Italian translation updated
Merge pull request #477 from bartokk/master

Italian translation updated
[l10n] Swedish update of .desktop strings