cstats fixes, improvements on IP Traffic and QoS pages
* cstats: since cstats can keep track IP traffic for a limited number of
addresses on its database, when an address is added to the "Excluded IPs"
list (admin-iptraffic.asp), its traffic history gets purged (makes room
for another/new address to be tracked).
* IP Traffic: previously, the "Details" page (renamed to "Transfer Rates")
used different conntrack files under /proc for K24 and K26 builds, in an
attempt to consider any/all IPv4 + IPv6 connections known to the router.
This version sticks to IPv4-only until we figure out how to properly do that.
* IP Traffic: added a "Monthly" history page, many visual improvements,
added "helper" links/shortcuts from/to IP Traffic and QoS pages.