masks: first steps for restricted masks edit mode
masks: implement restricted edit mode

you enter restricted edit mode by CONTROL-click on the "show masks and edit"
icon. in restricted edit mode shapes are protected against accidental deleting,
shifting and enlarging/shrinking. you can still act on single nodes and on the
feathering border. main purpose: eases fine-tuning of shapes (esp. path shapes).
Merge branch 'mymasks'
blending: repair most of blendop parameter sets that got broken recently

breaking of parameter sets did happen when legacy history stacks were
converted to the new structure by the recent development branch. this commit
allows darktable to automatically fix most of the broken blendop parameter
structures (see bug #9466)
Metadata viewer: indicate that the focal length is given in milimeters
Metadata viewer: don't display invalid/unusable "focus distance" values
colorize module: fix color conversion matrix

the old version had a wrong matrix which caused a color shift - visible
e.g. as a blue tint when saturation is set to zero. of course legacy
history stacks are preserved and process as before.
cacorrect: fix a segfault for very small buffers.
color picker: backtransform picker coordinates; fixes #9482

coordinates of local color picker need to be transformed back from the preview
image to the module in focus, else we pick completely bogus spots if distorting
modules are in action.
color picker: better account for invalid local color picker data in several places

if the local color picker is positioned outside the module's image area it can not
deliver valid data. take appropriate action in this case (depends on where we use
the color picker).
blending: add option to toggle polarity of drawn mask

this is needed to effectively extend a parametric mask by including or
excluding specific parts of an image.

to include parts: switch combobox combine to "inclusive" and make sure
polarities of drawn mask and parametric mask channels are set to negative.

to exclude parts: switch combobox combine to "exclusive" and make sure
polarities of drawn mask and parametric mask channels are set to positive.

use "inclusive & inverted" or "exclusive & inverted" to get an inverted mask
if needed.

the "toggle polarity" button (circle with black&white) can be used to quickly
toggle between inclusive and exclusive mode.
Add two more guides to c&r, perspective + metering
fixes bug #9487
Fix a crash when live view is not supported ...

... and live view is switched on and off again
graduatednd: fix (marginal) bug in distance calculation
Merge branch 'master' of ssh://github.com/darktable-org/darktable
fix a few memleaks
Update Polish translation
cache: make stats work on legacy compiler + arch.
Merge pull request #251 from jktjkt/metadata-viewer-tweaks

Metadata viewer tweaks