Activate GUI for watermark layout.

It is now possible to layout properly a watermark whose scale is
computed based on the larger or smaller border. This make it possible
to use a watermark inside a style an apply it into images in portrait
and landscape mode with proper layout.
Upgraded and reviewed Spanish translation

 I have fully reviewed the Spanish translation, fixing typos,
 improving grammar and the language used.
Fix: snapshot + gnd, cliping, ... #9329
usermanual: add missing file lighttable_directory.png
don't crash on malformatted TIFF file

In case a file was alraedy rejected by GraphicsMagick, it's not a good
idea to try open it with our handmade imageio routines like TIFFOpen().
Let's take GraphicsMagick as a last resort if available.
If node stEvt:softwareAgent not found, skip as not a lightroom xmp.
Proactive fix to avoid a crash trying to dereference a null pointer.
Merge branch 'fix-crash-lr-import'

* fix-crash-lr-import:
  Proactive fix to avoid a crash trying to dereference a null pointer.
  If node stEvt:softwareAgent not found, skip as not a lightroom xmp.
adobe_coeff: Nikon Coolpix A same as D7000
white balance: make it relative to daylight balance

assuming that has been created wrt CIE daylight.

the end result is somewhat similar to ufraw, numbers vary wildly
but in principle it's relative to something constant and not to
camera white balance anymore.

also removed second temperature slider.
bauhaus: also reset to default on double click if -1 entry was selected.
Merge branch 'watermark-layout-options'

* watermark-layout-options:
  Activate GUI for watermark layout.
Update french translation.
whitebalance: default temperature is daylight wb
allow zoom under the "fit to screen" limit
smaller zoom steps under "fit to screen"
Merge pull request #208 from darktable-org/gnd_fix

Gnd fix