Fixed installation of Lua scripts

The 'scripts' subfolder was not added to the toplevel CMakeLists.txt
Removed some outdated and not useful documentation
Changed SpawnArea and TriggerArea to components of Entity

Well, first visible change is that everything just gets longer to read.

Reviewed-by: Yohann Ferreira
Changed Item to a component of Actor

Items also have positions, so the ItemComponent only makes sense as part of
an Actor. Later on it will probably be part of an entity that also has an
ActorComponent.

Since it was annoying to update all the places where items were created,
I've introduced a function for this.

The component types are now prefixed with "CT_" because I wanted to introduce
an 'Item' namespace which would otherwise be conflicting. The component types
enum isn't used much in the code so it can look a bit ugly.

Reviewed-by: Yohann Ferreira
Changed Effect to a component of Actor

Reviewed-by: Yohann Ferreira
Changed NPC to an NpcComponent added to a Being