[Feature] Finish quest chain editor

[BAndysc]

Summary

Quest Chain Editor should be a new module that allows user to easily manipulate quest chains in form of graph, without touching SQL at all.

A lot of work has been done already on drawing graphs and producing SQL in the project https://github.com/BAndysc/WoWDatabaseEditor/tree/master/WDE.QuestChainEditor and https://github.com/BAndysc/WoWDatabaseEditor/tree/master/QuestChainTest

There are however still some things missing before it is usable and production ready, mainly:

• ensuring the chains are properly loaded from DB
• ensuring that chains are properly serialized to SQL
• ensuring that loading quest X will load ALL connected quests
• adding undo/redo ability

Nice to have:

• copy/paste/cut option
• multiselect