[Refactoring] Add Observer abstraction

[nbrugger-tgm]

Observer abstraction

At the moment lists are handled by the Observer class using a workaround. But this Workaround changed the logic of the "normal" property observing logic. Also the structure is not expandable.

Therefore a structure should be created that there is a super-type for Observers and multiple observer implementations can exist

Example structure

AbstractObserver (interface)
├─ ActionObserver (abstract)
│  ├─ MapObserver
│  ├─ ListObserver
├─ ObjectObserver

As this is a fundamental change many systems such as ReactiveController will be affected.

[nbrugger-tgm]

Changes implemented

The changes are implemented.

Additions

The Proxy system had to be reworked too as the systems were tightly bound.

New Proxy Structure:

ProxyEngine (abstract)
|- ReactiveProxyEngine
|- ListProxyEngine

New/Changed therms and classes

Therm	Description	Usage for Users	Final form
ProxyEngine	The class to base ProxyEngines off. Catches proxy calls and distributes them		✔
ReactiveProxyEngine	A ProxyEngine for ReactiveProxies		✔
Proxy	A class that forwards calls to an ProxyEngine		NOT A CLASS
ProxyCreator	A ProxyFactory	✔	❌
ReactiveProxy	A Proxy that makes an object reactive	✔	✔
ReactiveWrapper	Warps a plain object to provide a Reactable implementation. Warning: Does not calls react automatically! Thats what ReactiveProxies and ReactiveSubject are used for	〰	✔