Unify dictionary construction for commands?

[tinchodias]

These are some ways the dictionaries that will be transformed into json are created:

	self command: (OrderedDictionary new at: #ismaster put: 1; yourself).

	command := OrderedIdentityDictionary new
		at: #create put: aString;
		yourself.

	dict := {
		'insert'->collectionName.
		'documents'->{newDictionary}.
		} as: OrderedDictionary.

I see it's justified to use an ordered dictionary for commands: e.g., it's wrong to execute the command with a json that has 'document' before 'insert'. But I don't see a reason to use the Identity one.

I create this issue because of a small discussion in issue #60.