argparse instead getopt

Hi all,
I replaced [getopt](http://docs.python.org/2/library/getopt.html) to [argparse](http://docs.python.org/2/library/argparse.html).
argparse allow write less code, show better help message and be easy to use...
I make commands (setval, issue, send and etc) as sub-commands
Now, help message looks so:

    usage: ngccc.py

    Next-Generation Colored Coin Client Command-line interface

    optional arguments:
      -h, --help  show this help message and exit

    subcommands:
      import_config  Import json config.
      setval         Sets a value in the configuration.
      getval         Returns the value for a given key in the config.
      dump_config    Returns a JSON dump of the current configuration.
      addasset       Imports a color definition.
      issue          Starts a new color.
      newaddr        Creates a new bitcoin address for a given asset/color.
      alladdresses   Lists all addresses for a given asset/color.
      balance        Returns the balance in Satoshi for a particular asset/color.
      send           Send some amount of an asset/color to an address.
      scan           Update the database of transactions (amount in each address).