…rom lists store

Not complete yet, just work done so far.  So test fails are expected still.

…Entity instances

- This string is used in rest requests retreiving entities for a given set of ids.

- also adds getEntitiesByIds selector and resolver.

With the use of  Redux.combineReducers  (via wp.element), the root state is actually a plain object with all the individual state slices implementing immutable.js.  In the tests I wrote, I was considering the entire state being an instance of Immutable.Map when that’s not actually the case!  So the tests passed for that assumption but not really testing real-world use-case.

Although we _could_ implement our own (or a redux-immutable) combineReduceers to make the root state an Immutable.Map()… that could have repercussions down the road for other bolt-on things exposed by WP for the data stores that expect the state root to be a plain obejct.  I figured it’s safer and more future proof to simply have the state slices that matter using immutable (as the reducers/selectors are what will trigger re-renders).

…he item

- existing event-attendees block (and related support components) needed updated to account for model entities no longer being a Map but rather a simple array (which imo is easier to work with).
- After initial user monkey testing in the browser console, I discovered some other fixes needed in both the new code and automated tests (likely more to come as I keep testing).

The index is still in the state, but exposing this level of granularity to clients created potential problems with order of execution etc.   This state tree is more of an optimization (lookup) trick for internal use so I’ve taken care of automatically changing its state internally via the reducer rather than controlled via its own action.

- its possible that  a relation is never indexed because its always listed as a relation to another entity in the state.  So we need to have reverse lookup implemented for both getRelationAdditionsQueuedForModel and getRelationDeletionsQueuedForModel for those cases where client is looking for relations using a modelName that is not a key in the index.

…mpty Map for the model

- this includes changes to `Immutable.Set().delete` usage.  It accepts the _value_ to delete and that is much simpler than providing the key (although key seemed to work).
- this includes some faulty logic fixes that was deleting from relation index unexpectedly and making sure tests were updated to catch that.

- pop is more performant becuase the array does not need re-indexed.  There’s no need to retain order here so `pop` is sufficient.

# Conflicts:
#	assets/dist/build-manifest.json
#	assets/dist/ee-components.622f86c8649619cbcbcb.dist.js
#	assets/dist/ee-components.7d6c99591998d2eae4c0.dist.js
#	assets/dist/ee-components.b72fa352434166ef52be.dist.js
#	assets/dist/ee-data-stores.67b185e1920ba24c7431.dist.js
#	assets/dist/ee-model.7f810d358d08f82e088b.dist.js
#	assets/dist/ee-model.93606ab921bb65bfe8e0.dist.js
#	assets/dist/ee-model.b08f7f3ee436d1dbb468.dist.js