ZENGINE: Use spaces in doxygen comments for alignement instead of tabs
ZENGINE: Create an instance of ScriptManager inside ZEngine
ZENGINE: Create ResultAction base class and ActionAdd child class
ZENGINE: Convert ScriptManager methods to use ResultAction classes logic
ZENGINE: Comment clarification for ScriptManager methods and helper structs
ZENGINE: Create global state accessor/mutator methods for ScriptManager
ZENGINE: Create ScriptManager accessor for ZEngine

Having the ScriptManager as a member variable forced it to be const,
which prevented any non cont methods to be used. Thus, ScriptManager is
created on the heap and disposed after use.
ZENGINE: Fix include for singleValueContainer.cpp
ZENGINE: Move test functions out of video.cpp and into their own file

The file only exist to hold the code. The actual tests will be
moved to an appropriate location later.