Refactor how current cart id and current user token are obtained

[pkarw]

What is the motivation for adding / enhancing this feature?

In many places we're taking this data from localStorage - by the same time having it in the user.state and cart.state. What we should just make sure of is that these information are properly loaded from localStorage first

Example: https://github.com/DivanteLtd/vue-storefront/blob/2328ec8f8942cbdcc6b371120ba0984553a50ee1/core/client-entry.ts#L241

We should find all the current-token and current-cart-token references and do refactoring to get the info from Vuex getters.