removed GPC library due to its unacceptable license. Using the great and powerfull kbool library insteed

Fixed all related files also.

B.O.M. generation still have a minor problem wih this.

 for backanno.cpp, a better candidate for searching.

wxProcess::open does not work under windows (the process stays in background mode), wxExecute is still used under windows
Minor other changes

eeschema: code cleaning. SCH_ITEM class used for all schematic items in eeschema. Files reorganization.