FoF code

[manonramel]

I implemented the code for the Friends-of-Friends algorithm.

The idea is to:

• Use the FoFCatalogMatching function which returns a Table converted into a pandas dataframe, composed of 3 columns: "row_index", "catalog_key" and "group_id".
• Replace the "catalog_key" column with "is_cat1" column filled with booleans (True if the object belongs to catalog 1, False otherwise) to optimize the code
• Use the pandas method groupby and make a loop over the sub-tables to store the row indices of catalog1 and catalog2 components in two different lists
• Combine the two lists of indices in one list representing the group and return the groups.

I tested this code in one tract, using truth and object catalogs. It approximatively takes 15 minutes to execute.