#4 SPC additions

[Sebastián López]

Arthur Dijkstra::

These are the function sthat are not developed yet:
CHART_EWMA: (None, data.prepare_data_none),
CHART_CUSUM: (None, data.prepare_data_none),
CHART_THREE_WAY: (None, data.prepare_data_none),
CHART_TIME_SERIES: (None, data.prepare_data_none)}