added the example gen_gerber_and_drill_files_board.py in demos, which shows how to do that.
Fix a Printf format issue (shown in Debug mode) in Libedit (%d used for a size_t, changed in %zu)

Add a python script example in demo folder to create various plot files from a board. Fix also some issues in plot controller helper class.
Important note: from a python script one cannot plot the palge layout, because the page layout template file is not stored in the board file, but it is part of the project.
Because when using a python script, the project is not loaded, the page layout template is not known.
Trying to plot it crashes the script.