Implement storage statistic printing on console

[ataffanel]

Until now the storage subsystem was quite opaque in the sense that it is not possible to inspect its state and how much space is being used.

This PR implements a way to print storage statistics on the console. The printing is controled by setting 1 the parameter "system.storageStats". The printed values looks like:

STORAGE: Used storage: 46 item stored, 1394 Bytes/7168 Bytes (19%)
STORAGE: Fragmentation: 60%
STORAGE: Efficiency: Data: 387 Bytes (5%), Keys: 869 Bytes (12%), Metadata: 138 Bytes (1%)