Make data type row in CSVs optional

[contactashish13]

Most data sets (e.g. https://www.quandl.com/api/v3/datasets/WIKI/AAPL.csv) do not provide the data type of the column as it is self-explanatory to humans. But because the plugin requires the data type to be specified, this prevents users from hooking directly into an API or a remote URL that does not provide the data type. We should make such integrations easier.

[DanyCaissy]

@contactashish13

Do you think it would still be possible to do so while ensuring that existing charts using the previous data are still compatible?

[contactashish13]

@DanyCaissy yes, the intent would be to make it backward compatible.