Get creator by name fix

[iLLiCiTiT]

Issue

• Maya's Referrence loader and Blender's Layout loader are creating instances during loading and are expecting that avalon.api.create can work with only family which is not possible since PR in avalon-core

Suggested solution

• implemented function get_creator_by_name that returns creator plugin but it's name
• loaders have defined creator name that will be used to create new instances and use get_creator_by_name to use it

Note

The function get_creator_by_name returns None if none of registered creator plugins match to entered name and loaders will raise an error if that happens. Should the error be raised? Should be raise inside the loader or inside get_creator_by_name?

🏴	Pype 2.x PR
pype	#979