Update kamaki.cli.cmds.pithos class names (pep8)

Renames:
_pithos_init --> _PithosInit
_pithos_account --> _PithosAccount
_pithos_container --> _PithosContainer
_source_destination --> _PithosFromTo
_pithos_group --> _PithosGroup
Change kamaki.clients.cyclades class names

Names are changed for uniformity. Backwards compatibility is kept,
(old names are not dismissed)

Renames:
CycladesRestClient --> CycladesComputeRestClient
CycladesClient --> CycladesComputeClient

Users can still import and user CycladesRestClient and CycladesClient
Move default argument initilization to kamaki.cli

Default arguments where set in kamaki.cli.arguments using the
global variable "_arguments". This was a semantic mistake, a
pep8 violation and arguably bad style.  The "_config_arg"
variable was also global and auxiliary to "_arguments"
initialization.

The "_argument" and "_config_arg" global vars are removed from
kamaki.cli.arguments. The initialization is now an internal
proccess in the "main" function of kamaki.cli, which is the
method responsible for setting up all kamaki interfaces.