Change LEAF explorer to one on correct block chain

Change LEAF block chain explorer to one that is on correct block chain.

There was a required change - adding Kimoto's Gravity Well to Leafcoin, and it was applied at block 18818 (in "gravity fix - 3"), but not all updated - so there is a block chain fork.

Leafcoin source: https://github.com/leafcoin/leafcoin
More info: https://bitcointalk.org/index.php?topic=430091.0