Good practices to discuss in the course

[hageboeck]

A compilation of suggestions from #78

• Interfaces -I.3 (singletons) as well as I.11 & I.13 (avoid raw_ptr ownership transfer, avoid passing arrays without length)
• Errors - E.6 use RAII
• Classes - C.131 Avoid trivial getters/setters
• If you have a debate about how to do something, check core guidelines
• When to use free functions (anonymous namespace) and when member functions
• Keep headers clean, low number of includes? (Implement comments from #428 #508)
• Discuss SOLID principle at the end of OOP