Update tenders and networks

[georgiana-b]

TED data is changing from one release to another.
Tenders receive new lots and bids, some of the initial buyers are removed, new ones are added, prices change, etc.

This PR adds functionality to incorporate all these changes in Elvis. Specifically:

• updating the tenders, bidders, buyers as they are being added, changed or removed from one version of the data to another
• updating the networks accordingly: removing the actors that were removed, adding the actors that were added, recalculating those that received new tenders
• updating the clusters accordingly: removing from the cluster the nodes that were removed, recalculating the cluster from the new tenders of the nodes that are remaining