lighttable: support drawing of arbitrary custom meta data as burn in.

use `plugins/lighttable/draw_custom_metadata=TRUE' in your darktablerc
and darktable will display the contents of a text file with the same name
as your image but .txt suffix as on overlay in one-image-per-row mode.
opencl: add GeForce GT330 to the device list
masks: a more consistent icon for "inverted" in masks manager
usermanual: on the mask manager panel
opencl: remove superfluous asterisks from list of nvidia gpu's
dithering: remove nonsensical core-option to disable dither for center view
[l10n] Swedish update: synchronise
Update French translation.
Italian translation updated
Merge pull request #284 from bartokk/master

Italian translation updated
usermanual: updates and corrections
update of dutch translations
basecurve: ported thorsten's scattered data dumper to c.

next steps would be fitting the monotonic hermite.
basecurve: added gnuplot script to visualise output.
basecurve: added makefile.
basecurve: fit our spline to the data.
basecurve: nicer plot and dump line for iop/basecurve.c into fit.dat
basecurve: write to files explicitly.
usermanual: updates
basecurve: enable filtering by model/maker if desired.