Fix bugs and add more ways to work with AssetReference, AssetReferenceList and EntityReference from scripts. Most notably you can now flexibly work with EC_DynamicComponent attributes of these types. The FromQVariant logic was completely missing for all of these types. Also working directly with component attribute (eg. mesh.meshRef, placeable.parentRef) is now a lot more flexible and accepts more inputs (we can deduct what you are intending to set in a lot of cases). Added tests for creating all dyn comp attribute types and made extensive tests for AssetReference, AssetReferenceList and EntityReference. Fixes #748.