change type of scalehandle_new and h_master. Document some structs in g_all_guis.h and change some field sizes.

remove canvas/glist arg in a bunch of recently added iemgui functions, and introduce iemgui_draw_move & iemgui_draw_config

big refactoring #11 : replaced %lxOBJ by x%lx and removed nlet_tag from all iemgui, among other smaller changes

big refactoring #10 : simplifying the _draw_new, _draw_select, _new, _dialog methods, among other things

big refactoring #8 : fusion of [hsl] and [vsl] together, and fusion of [hradio] and [vradio] together