Statistics collection added

 - added statistics counters and tests
 - collection configurable through configSubsystem

Change-Id: I0b292174789fbb39ff7abd25fec9b53b35ff7927
Signed-off-by: Marian Adamjak <marian.adamjak@pantheon.sk>
Signed-off-by: Michal Polkorab <michal.polkorab@pantheon.sk>