Support for EMap

[rettenbs]

It would be nice to have a container that supports key-value pairs where the value is another eType.

I tried something like this, which seems to work for inserting elements:

class Map(dict):
	def insert(self, key, value):
		super().__setitem__(key, value)

class EMap(ECollection, Map):
	@classmethod
	def create(cls, owner, feature=None):
		return cls(owner, feature)

	def __init__(self, owner, feature=None):
		super().__init__(owner, feature)

EReference(upper=-1, derived_class=EMap)

However, I am not sure if ECollection is the corect base class and if there are any other things that need to be considered, i.e. to notify the owner and update the opposite.

I think, for removing it would be possible to use pop.