Never use selected_images in control_jobs (remove/delete).

Indeed between the time we click on delete and the time where the
SQL statements get executed there is a small window where the
user could click on some images and change the selection.

This could even been far more a problem with scripts like Lua.

Instead of using the selected_images table we now properly get the images
to work on from the list associated with the job.

Take the opportunity to refactor some code for better sharing. This fix
an obvious bug where in dt_control_delete_images_job_run we where getting
only the first images for checking for duplicates.
Italian translation updated
usermanual-it: add chapters 1 and 2
Prevent users from unintentional image overwrite
Merge pull request #409 from fedelibre/usermanual-it/start

usermanual-it: add chapters 1 and 2
Early bailout in calculator on empty formula
Add support for calculator formulas in conf

This is needed for cache_memory to be a nice looking value in the XML*.
If it turns out to be too slow we have to revert and remove the formula
from the XML file*.

* data/darktableconfig.xml.in
Fix overexposed borders to be float instead of int
Remove hardcoded default settings from the code

... these are all in the XML and default darktablerc now.
Merge pull request #408 from bartokk/master

Italian translation updated
Fix wrong default for filmstrip height
Fix crash in calculator on malformed input
Prevent overflow when parsing numbers

at least make it happen with much bigger numbers only.
imageio: don't accidentally use libraw
Merge branch 'fix-race-condition'

* fix-race-condition:
  Never use selected_images in control_jobs (remove/delete).
Attempt to fix compilation issue.
Another attempt to fix compilation issue.
masks: improve status update of the various shape create icons; should mostly fix #9748

concerning the mask manager: this fix still does not make the icons' on/off status
always reflect the creation mode, namely if you interrupt shape creation by right-click.
however, now shape creation continues to work as expected: click once on the desired shape icon.
Remove: dt_iop_load_preset_interpolated_iso as not used.
New routine to check if a directory is empty.

Preparatory work for #9732.