Encourage passing constructors to getStore and waitFor instead of strings

[mridgway]

For dependency mapping, it's better to require a store and pass the constructor to getStore and waitFor instead of store name string. At the very least, the readme should be updated to reflect this and use constructors instead of strings in the examples.

It may also be better to remove string capabilities in getStore and create a separate function getStoreByName for accessing stores by name.

[ptomasroos]

I fully agree with this! I will take a look on it tonight.