Smart filter support.

[poljar]

The Python script somewhat supports smart filtering like the IRC plugin does, it is a bit flaky but often times it works well enough to hide massive amounts of joins/leaves.

To support this we should track the activity of members, e.g. every time we fetch a member to render an event that is send by that member we should save a timestamp of their last activity. Then based on that timestamp add a smart filter tag when we render membership events.