[UI] Form widget to assign a series

[amercader]

Create a form snippet for the in_series field:

• Include a select input with the available Dataset Series datasets (i.e. the ones the use can update, see in_series validation #1, minus the ones already assigned)
• Show the current series the dataset is member of, with a control to remove it from the series
  Under the hood it should send the same value as the multiple_text preset.