[Code health] Rename members of `LocalDataStore` classes

To improve readability, recommending the following changes to `LocalDataStore`. Sharing initial thoughts here:

* `surveyStore` -> `surveys`
* `userStore` -> `users`
* etc.

Then, in each local data store, functions can exclude the qualifier (survey, locationOfInterest, etc), since they data store name already qualifies them. Also, we should be consist and use meaningful verbs to clarify what each fun does. For ex, in `LocalSurveyStore`:

* `surveys()` -> `loadAll()`
* `getSurveyById()` -> `loadById()`
* etc

Lastly, replace `surveyDataStore` alias with direct reference to `localDataStore.surveys` to remove ambiguity.

Example usage:

* `localDataStore.surveys.loadAll()`

@scolsen Wdyt?