banlist: add more banlist infos to log / add GUI signal

• to match the peers.dat handling also supply a debug.log entry for how many entries were loaded from banlist.dat and how long it took
• add a GUI init message for loading the banlist (same as with peers.dat)

• move the same message for peers.dat upwards in the code, to be able to reuse the timing variable nStart and also just log, if our read from peers.dat didn't fail