Bitcoin-Qt: never display own block count > estimated block count

• some users reported it as weird, that the estimated block count could be lower than our own nodes block number (which is indeed true and not good)
• this pull adds a new default behaviour, which displays our own block number as estimated block number, if own >= est. block count
• the pull raises space for nodes block counts in cPeerBlockCounts to 8 to be more accurate
• also removes a reduntant setNumBlocks() call in RPCConsole and moves initialisation of numBlocksAtStartup in ClientModel, where it belongs