added basic filtering to twitter.class

done differently than i proposed in #127.
* gets a list of all active mods (minus twitter itself)
* filter tweets that have a source that contains the name of an active
mod
* i suspect the modNameList() function in reclaim.php to be written
poorly. it might be a performance hog or cause other problems that i
don't understand. i jope some one who knows what he/she is doing can
have a look on that