source and attribution metadata from data library datasets are not copied when imported

[oriolbx]

When a dataset from the data library is imported into user account, the metadata source and attribution is not imported with the table. The user has to add the source and attribution metadata manually and then refresh to see the attribution on the map.
Steps:

1- Import dataset from data library:

2- When the dataset is opened, the attributions and source metadata from the dataset are not copied on the map:

3- The user have to add the attribution and source metadata manually with the "Edit metadata" option form the dataset, and once is added you have to refresh the dataset to see the attribution on the map:

I've been checking the CartoDB metadata and I have realised that the user_tables schema doesn't have the attributes source and attribution.

[iriberri]

cc @ethervoid

[ethervoid]

I'll take a look to it. Assign it to me

[iriberri]

The attribution and source parameters are stored in the canonical visualization of the Data Library sources. I don't know how this works, but if we're just recreating the user_table there's where we are missing it. :-) Not super urgent, but I think this is important because of the focus to data and attributions we are doing (now CartoDB.js adds data attributions directly to the maps).

[juanignaciosl]

Fixed: #6897.