Option to download uploaded stuff

[jbglaw]

Hi!

I've successfully used the rocketchat-exporter and noticed two things:

• When somebody leaves a channel, this shows up as an empty log message. Would be nice to have an actual indicator of the action, like adding this to a new CSV column.
• If somebody attached/uploaded an image for example, that'll also show up as an empty message. Would be nice to have an option (probably also in a new CSV column?) to have a reference to the download URL and to possibly automatically download that content.

Thanks, Jan-Benedict