Refactor and Improvements

[brunomikoski]

Changed

• Renamed the Collectable for CollectionItem this has several changes in multiple parts of the code, I tried my best to keep compatibility with the old version. CollectableScriptableObject still exists but has the obsolete flag on it to avoid breakable changes.
• Add IsValid to IndirectReferences to check if has valid data before being used
• Refactored ResourceScriptableObjectSingleton to fix some warnings
• Fixed the GetEnumerator from Collection warning
• The CollectionRegistry now will only load Collections that are inside an active Assembly.
• Exposed the Collections list on the Registry
• Simplified the CollectionItem Dropdown (removed the type grouping)
• Multiple QoL improvements on the codebase.

Added

• A new information on the Collection custom editor to show the base class if is different from the collection type (Disabled for now)
• Exposed the namespace to be customized by the custom static file
• Added support of multiple collections of the same type on the registry, the CollectionItemDrawer will display a Collection dropdown if more than one collection for the same type of item is available

Fixed: #63
Fixed: #61
Fixed: #60
Fixed: #59
Implemented: #51