Integrate wxFileHistory, add missing header files to fix Linux build, initial search path work, and general housekeeping.

eeschema: code cleaning, comments added, and the true number of sheets and sheets numbers in complex hierarchies

All: cleaning code to draw/plot texts (work in progress). Eeschema: italic and bold texts and labels allowed
(plot functions not yet updated for bold texts)

Improved grid implementation, 3D viewer debug assertion fix, moved drawpanel.cpp to common library, and added WinEDA_Appl declaration.

areas can be now filled using solid polygons, or using segments to fill areas inside polygons.

Dutch language update
 - 182 strings left
 - 100 fuzzy strings left

(more noticeable in eeschema)