Pcbnew: fix a minor bug: in zones with no net, only the zone clerance was used to created clearence,  regardless the pad or footprint local clerance.
Very minor other fixes.

This workaround was already used (bzr 4301, in file plot_board_layers.cpp) also to avoid similar crashes (uses 18 segments instead of 16 to approximate a circle by segments).
Minor code cleanup in dialog_plot.

Fix kicad_plugin.cpp coding style fully broken by commit 4887 (patch from Orson, AKA maciej suminski).

Changes introduced by the module editor are updated in GAL canvas.

Minor refactoring of PAINTER & RENDER_SETTINGS classes.

A couple of trivial accessors made inline

Fixes the bug that causes pcbnew crash, when there are multiple net classes and the plot dialog was opened.
Changed NETCLASS* to boost::shared_ptr<NETCLASS>.