Feat: Starting to implement the propagation of the confirmed flag (#440)

* Fix: fixed marshal/unmarshal of branch regarding finalized flag

* Feat: added confirmed propagation to branch dag

* Feat: added rejected marshaling

* Feat: added comment for SetBranchFinalized

* Feat: finished confirmed propagation

* Feat: private setters so one can not mess with the tangle

* Refactor: refactored some code

* Feat: linked branchmanager to tangle

* Feat: refactored confirmed propagation

* Feat: started to clean up the code / resort methods

* Feat: cleaned up more code

* Refactor: reordered methods