atomic code expert tool

This patch implements changes and features requested by @herdem and @pamuelle:

• change file permissions for doctest.h (now invisible) and tests.cpp (now locked)
• eliminate redundancies for tests.cpp between template and solution (always take template)
• introduce config files for better control over included files, e.g. the JuliaSet assignment could now use the following config file, since it does not require timer.h:

{
	"includes": [ 
​
		"MatplotlibC++/matplotlibcpp.h"
	]
}