Mixin proposal for resource components injected with va prop

[sgobotta]

We're currently handling custom components the following way:

1. A custom component is passed to Resource by a user
2. Resource injects a va props into this component with crud functionality
3. The user accesses it's props to use the crud functions, like this.va.fetchList

Gabi Buenou (aka @glmaljkovich) suggested mixins to inject this functionality. This would not only provide a facility to the user (usage be like: $va.fetchList), but would also help decoupling the binding utils from the resource utils: more information in this WIP