Set default arguments of blockchain_list_blocks to 0 -20
Set default arguments of blockchain_list_blocks to 0 -20

Now the default behavior of blockchain_list_blocks is to list the last
20 blocks produced.

camponez/bitshares,drltc/keyid,bitshares/bitshares,bitshares/bitshares-0.x,camponez/bitshares,camponez/bitshares,FollowMyVote/bitshares,FollowMyVote/bitshares,bitshares/bitshares-0.x,dacsunlimited/dac_play,bitshares/bitshares-0.x,frrp/bitshares,jakeporter/Bitshares,frrp/bitshares,denkhaus/bitsharesx,denkhaus/bitsharesx,RemitaBit/Remitabit,RemitaBit/Remitabit,jakeporter/Bitshares,FollowMyVote/bitshares,bitshares/bitshares,RemitaBit/Remitabit,bitshares/devshares,denkhaus/bitsharesx,frrp/bitshares,dacsunlimited/dac_play,bitshares/bitshares,RemitaBit/Remitabit,dacsunlimited/dac_play,dacsunlimited/dac_play,bitsuperlab/cpp-play,FollowMyVote/bitshares,RemitaBit/Remitabit,frrp/bitshares,bitshares/bitshares,dacsunlimited/dac_play,RemitaBit/Remitabit,camponez/bitshares,bitshares/bitshares-0.x,bitsuperlab/cpp-play,FollowMyVote/bitshares,drltc/keyid,camponez/bitshares,FollowMyVote/bitshares,drltc/keyid,frrp/bitshares,bitsuperlab/cpp-play,bitshares/devshares,Ziftr/bitshares,denkhaus/bitsharesx,jakeporter/Bitshares,drltc/keyid,Ziftr/bitshares,camponez/bitshares,bitshares/bitshares,Ziftr/bitshares,dacsunlimited/dac_play,bitshares/devshares,bitshares/devshares,bitshares/bitshares-0.x,jakeporter/Bitshares,bitsuperlab/cpp-play,frrp/bitshares,bitshares/bitshares-0.x,bitshares/bitshares,bitsuperlab/cpp-play,bitshares/devshares,Ziftr/bitshares,bitsuperlab/cpp-play,jakeporter/Bitshares,bitshares/devshares,jakeporter/Bitshares