[v6r8]FIX: dirac-rss-set-token, NEW: Statistics module

THIS PR REQUIRES AN ACTION ON THE DB: 
Delete *unused* table `ResourceManagementDB.PolicyResultLog` and generate new ones with `dirac-rss-setup`

This PR incudes:
* a fixed script dirac-rss-set-token, broken in the current release.
* a module named Statistics which will be used in the future to provide detailed information from the History of the elements ( on this PR: is not used within DIRAC, but will be on LHCbDIRAC )