only create a date dimension when needed, and do not raise exception otherwise. some dataset could share date dimensions
typo fix: hardwritten data in columns.py code...
change the identifier of labels. there was a bug
fix a pb with labels: label on attribute and on connection point are different
fix a bug in get_columns: get_class_mebers returns a list of tuples and not a dict
use a custom csv file writer, to handler unicode; rewrite every file overture with context manager
add a formatter module to help formatting date and null values for GD API
properly format dates and null values in archiver. requires the list of dates and datetimes in the dataset
change the way some methods are called in dataset.py, connection.py and schema.py, to be conform to new archiver arguments
Merge branch 'mvdb/ANA-423/date-dimension-already-exists' into mvdb/hot-bugfixes

Conflicts:
	gooddataclient/dataset.py
	gooddataclient/formatter.py