Added index and PK. Also fixed purgeLogs.
Purging once a day is enough.
fix for order
11 -> 12
Fix for date inserted (can be null)
Fix for date inserted
Beautyfication
Removing every 6 hours (blocking operation, might take longer)
Merge pull request #1988 from fstagni/fixForLogsTablev6r11

[v6r11] Fix for ProxyDB_logs table