Basic export framework and command line interface

[Lars Butler]

[et=16h]
[at=9h]

The actual export action itself (for a particular artifact type) will need to be custom written for each type. The scope of this bug just includes the basic interface and initial framework bits.

---------------------------------
Command line interface
---------------------------------

A few new command line options will be added:

--list-calculations:
  List completed calculations for the current user
  This command prints a table of calculation ids and descriptions

 --list-outputs <calculation id>:
  List outputs/output types available for the given calculation id

 --export <result id> <output dir>:
  Export a given set of out puts to the specified output dir

--------------------
Example usage
--------------------

$ openquake --list-calculations
7: Disaggregation for Zürich
18: Classical PSHA for my garden
1283: Uniform Hazard Spectra for the state of Iowa

$ openquake --list-outputs 1283
686: uh_spectra

$ openquake --export 686 /home/lars/uhs_data/iowa_uhs/
# print some message about which files where created and where

----------
Export API
----------

The following basic API functions are required for the above CLI options.

def get_calculations(user_name): # see --list-calculations
  """Get pairs of (oq_calculation_id, description) for the specified user."""

def get_outputs(oq_calculation_id): # see --list-outputs
  """Get pairs (output_id, output_type) for the specified calculation."""

def export(output_id, target_dir): # see --export
  """Export the specified output to the specified location."""

def print_result(data):
  """Utility method for printing the results of `get_calculation` or
  `get_outputs` in a nice way."""

[Lars Butler (lars-butler)]

Pull requests:
https://github.com/gem/openquake/pull/691
https://github.com/gem/openquake/pull/692