[Twitter user tweets] Handle refreshing a former collection

[boogheta]

We often want to restart a collection on the same set of users to only grab new tweets since the last data collection. To do so it would be nice to be able to restart:

• either from the former output directly (but maybe a bit heavy and inconsistent with the actual CLI arguments)
• or from the csv list of accounts with an extra column being the ids of the last tweet collected for each desired user (which we could easily generate from the former output). In this case the CLI would only need an extra argument giving the name of the column in which to find these last_tweet_ids

(followup #208)