Adding/Removing the abstract modifier on a class/trait

[tomzx]

Code	Level	Rule	Explanation
---	---	- Class	---
VXXX	MAJOR	-- Added	The method doesn't have an implementation anymore. It must be implemented by all class that inherit from it.
VXXX	MINOR	-- Removed	The method may have an implementation. Classes that inherit from it may not need to implement it anymore.
---	---	- Trait	---
VXXX	MAJOR	-- Added	The method doesn't have an implementation anymore. It must be implemented by all class that inherit from it.
VXXX	MINOR	-- Removed	The method may have an implementation. Classes that inherit from it may not need to implement it anymore.