Building with enhanced clang warnings indicated a large number of
instances with the warning:
`warning: zero as null pointer constant`
Recommended practice in C++11 is to use `nullptr` as value for
a NULL or empty pointer value. All instances where this warning
was encountered were corrected in this commit.
Where warning was encountered in dependency code (i.e. external library)
no chnages were made. Patching will be offered upstream.
At first we created the GUI in the code and so needed all the layouts
etc include to the code. Now when we are using UI files we don't need
all those included. So clean them up. Also use forward declarations
instead of includes in header files when possible.
Include guard naming fix (names starting with underscore+capital letter are reserved in C++, so we should not use those)
Codeblocks project file update
Add "Authors" and "License" items to the Help-menu. When selected, these items open simple text file viewer dialog. The AUTHORS and COPYING files are embedded to the executable and shown in the dialog.
