Historically the configuration used to be stored in layer's custom properties, but that does not scale
beyond simple rendering and so rule-based labeling introduced storage of configuration natively in XML elements.
That left us with two different ways of reading/writing labeling configurations. This work makes all configuration
to use native XML elements.
To keep compatibility of 2.x projects, reading of configuration from custom properties is preserved.
This commit also adds Python APIs for direct manipulation of labeling configuration through vector layer's
setLabeling() and labeling() calls.
This is necessary in order to be able to correctly translate between absolute and relative paths
deeper in the code - e.g. paths to SVG files used in marker or fill symbols.
Until now, relative paths were translated to absolute paths on the fly.
This is now changed - paths to files should be always absolute within QGIS objects - and paths
only get turned into relative when saving projects. When loading a project, relative paths
are translated to absolute paths immediately.
This should lower the overall confusion about relative/absolute paths within QGIS, and also
allow having different base directories for relative paths (e.g. QML or QPT files may use relative paths
to their directory - rather than to the project directory)
The geometry cache was only used for few geometry editing operations anyway. In earlier versions
of QGIS the geometry cache was also used by old snapping classes which have been replaced
by QgsPointLocator that also keeps a spatial index of geometries and it is not rebuilt on every re-render.
Reasons for removal:
- geometry cache was repopulated on every redraw of layers in editing mode, slowing down rendering
- data structure for the cache was a simple map with features accessed by their ID (no spatial index)
- the cache was only getting refreshed for the current view of the main map canvas (not a generic cache)
- not used for snapping anymore where caching was important to avoid roundtrips to data provider
It's only flipping a bool, and possibly in some circumstances
it's more efficient to add features one by one rather than storing
large number of features in a temporary list
Also cleanup API for addFeature(s) in QgsVectorLayer, by removing
the unused extra argument from addFeature() and be removing the
makeSelected argument from addFeatures() (code should be adapted
to manually select added features after adding if desired - this
was only used in a single place in the QGIS code and I suspect
this was unintentional in any case)
