Support ZNC playback module

[haarp]

This seems like a cool feature - I'll just copy this from the issue tracker of another IRC client:

The advanced playback module [1] makes it possible for IRC clients to avoid undesired repetitive buffer playback. IRC clients may request the module to send a partial buffer playback starting from a certain point of time.

Furthermore, the latest ZNC master [2] has support for persistent query buffers [3]. A client may choose to keep query buffers until they get explicitly closed in the GUI. This can be also easiest done via the same playback module to avoid undesired responses from ZNC [4].

The way it's supposed to work:

restart the client
    full buffer playback (/msg *playback play *)
    queries stay open
disconnect & reconnect
    buffer playback of channel & private messages received meanwhile (/msg *playback play )
close a query
    the appropriate query buffer gets cleared (/msg *playback clear )

[1] http://wiki.znc.in/Playback [2] znc/znc#598 [3] http://wiki.znc.in/Query_buffers [4] znc/znc#620

Cheers!