Update CUToolkit to permit store data locally when cds are unavailable

assigned to @bisegni

added CUToolkit enhancement labels

hen a CU fail to store data, for some reason, data need to be stored locally waiting to be restore as soon as ads will be available again.

data stored need to be preserved until space is available or for a determinate amount of space, in this case older data need to be discarded for make space for new data.

mentioned in issue #24 (closed)

mentioned in issue #36 (closed)

assigned to @amichelo and unassigned @bisegni