Removed SetCurrentClassName() (it was not used anywhere and less safe than SetCurrentClass()).
Added BOARD_DESIGN_SETTIGNS::GetDefault() to make some pieces of shorter and clearer.

Moved background color settings from GAL to RENDER_SETTINGS. Added RENDER_SETTINGS::TranslateColor() to convert between EDA_COLOR_T and COLOR4D.

Most of the changes are just adding GetDesignSettings() before every occurence of m_NetClasses.
More complex changes:
class_netclass.cpp - NETCLASS does not store the pointer to the parent BOARD anymore. Added function SetParams( BOARD_DESIGN_SETTINGS& ).
class_netclass.h - Removed GetTrackMinWidth(), GetViaMinDiameter(), GetViaMinDrill(), GetuViaMinDiameter(), GetuViaMinDrill() as they were refering to BOARD_DESIGN_SETTINGS anyway (they are not net class specific).
kicad_plugin.cpp - filters out empty nets (that are anyway not saved) when storing net class information. Previously it was done in NETCLASS::Format() function.

Moved a few one-liners of BOARD_DESIGN_SETTINGS class to the header file.

Moved menuCopy to CONTEXT_MENU copy constructor.

Cursor position is saved as a field in order to avoid drifting of items while they are being dragged and rotated/flipped.