Add a way to import curations

[liammulh]

• Add a simple, general way to import curations (either from CSV or JSON).
• Is this a purely internal thing? In theory this could just be Django fixtures.
• The data from the concordance spreadsheets is very dirty. For example, spreadsheet A has a cell that contains "4", but spreadsheet B has a cell that contains "4-field".
• If we import these curations, do we attach them to a user? Which user?