Fix #9951 (perimeter completely wrong with OTF on)

With OTF on and computation on an ellipsoid, the coordinates
were transformed twice(!) when measuring perimeter.
Fix #10202 (fix crash in graduated symbol renderer)
Fix #10514 (snapping marker visible even if not snapped to anything)
Fix #9733 (empty attribute table if showing just selected / visible features)
remove table and graph tabs only if there are no raster layers identified (#10376)
Fix #10524 (fix zoom to full)
[TRANSUP] pl: DateTimeEdit, others
Merge pull request #1440 from Cracert/i18n

[TRANSUP] pl: DateTimeEdit, others
Fix #10535 (legend symbol items for graduated symbol renderer)

The implementation used temporary symbols which are only valid
between startRender()/stopRender() calls and was breaking
also composer legend.
fix GDalTools overviews when clean and no levels are defined (#10538)
[processing] made postprocessing code more pythonic
[processing] some file restructuring
[processing] Do not throw exception if help file does not contain valid json
[processing] fixed wrong imports
[processing] more correct handling of nomodeler tag in scripts
#10433: Fix simplification of invalid and empty multipolygons
Merge remote-tracking branch 'alvaro/Issue_10433'
pal labeling: do not try to register feature if GEOS geometry is empty

This removes the debug noise from GEOS when it tries to compute contains() predicate
Labeling: use over centroid for polygon labeling by default
Fix #9148 (data-defined label positions with postgis)

A bit strangely, conversion of null variant with double type
to a double value is considered ok by QVariant