Review Media Manager refreshing and Repository access through MP or identifier

[hectorcanto]

The Media Manager is completely reloaded in some situations. This provokes a slow access to the Media Manager when the data is accessed through shared storage.

Also, when a reference to a Mediapackage object is stored - in operations for instance - there could be inconsistencies. Before data is modified the object should be reloaded.

Consequently, storing the MP could be a bad practice, better storing the identifier only.