Change classes to accept a $begin parameter
Change classes to accept a $begin parameter

Changed GraphTopArtists and GraphTopTracks class to accept a $begin
parameter that is used for limiting the query to tracks submitted after
$begin=timestamp.

Also changed GraphTopArtists to use $user->getTopArtists function
instead of Statistic::generatePlayStats.

foocorp/gnu-fm,foocorp/gnu-fm,foocorp/gnu-fm,foocorp/gnu-fm,foocorp/gnu-fm,foocorp/gnu-fm,foocorp/gnu-fm,foocorp/gnu-fm,foocorp/gnu-fm