LoaderPool:
Loader obtain(Loadable):
    If loader already obtained somewhere, return the existing Loader
    Create a new Loader if not obtained somewhere else.
void release(Loader):
    If no more listeners on loader, call destroy()

Loader:
void destroy():

void requestData():
    load from beginning
void requestNextData():
    board: load next page
    thread: reset new counter
int getUnread():
    return unread posts
long getTimeUntilReload:
    return time in ms until next reload


LoaderListener:
void onData(List<Post>, boolean append) can be called at any moment
    append: 
        true if the displayer should append to existing posts
        false if the displayer should replace existing posts
void onError(Error error) can be called at any moment
    404: it's gone
    EndOfLineException: no more pages