Module store

A store is a conceptual representation of your APP instance.
It is the outter envelop of the underlying entities involved.
APP does not define the concept of store per se but it is
a common way of naming and representing an APP instance.

A store is not really concerned about the meaning of members and
media resources however. All it cares about is 'meta-data' and 'content'.

A store needs at least one meta-data storage which will be used
to persist the representation of APP members.

A store can accept a second store which will be used to persist
media resources. If not provided the meta-data storage is then used.