For the "Around point" and "Cartographic" placement modes, this
adds a new optional setting for the maximum distance of the labels from
the feature. It's used together with the existing distance setting
to define a range of distances at which labels may be placed
from their corresponding point features.
This adds more flexibility to the placement for these layers,
ultimately allowing for more labels to be placed in busy maps.
When the layer is set to the "around point" mode, then label
candidates which are closer to the point will always be prefered
over those which are further away.
When the layer is set to the "cartographic" mode, then the default
behavior is also to prioritize closer labels. A new combo box
allows users to control the priority, with an option for
prefering position ordering. If this option is set, then candidates
at the corresponding positions (eg top left) are preferred regardless
of how far they are from the point, with the labelling falling
back to alternate positions only when no labels can be placed
up to the maximum label distance.
Sponsored by Rubicon Concierge Real Estate Services
The old sip based approach to handling property -> getter/setter
conversion is broken on sip6, so move the patching into Python.
Also fix incorrect checks in tests, and add additional test
for compatiblity code.
