add feature to choose the property name of the primary key of collection

[cHullaert]

Based on the model of createDb method on the inMemDbService in the BackendService, it's possible to define on the Service the method defineId which takes the collection name in parameter and returns the property name of the key.

By default, the behaviour of the component still unchanged since if the method is not defined the whole collections used the id name.

It is useful to link to an existing model domain

specifications is added
raw Angular Http w/ override id service
can get heroes
can get heroes by uuid

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[cHullaert]

I signed it!

[cHullaert]

Arf maybe I should create my merge request on more-dev branch instead of master..

[wardbell]

I think this is a good idea. It's an extension I've wanted myself and had intended to do something like this and along the lines of the id handling in @ngrx/entity.

I don't know when or if it will happen. I'm keeping your PR around as a reminder of what could be.

You may want to fork this library for your own needs.