"Join" tasks missing from collaborators tab

[saracarl]

If someone joins a project, they should show up in the collaborators tab as a collaborator (with zero time if they don't actually contribute).

The joined deed also needs to show up in the exported spreadsheet of activity.

(We also need to test/ensure joins are in the overnight activity email -- SU on CWRGM says she's missing them.)

[benwbrum]

The joined deed is logged if site visitor (with no account) visits a collection homepage, then signs up for an account.

[benwbrum]

It looks like the collaborators tab only pulls the list of users from deed types of transcriptions or corrections: https://github.com/benwbrum/fromthepage/blob/development/app/helpers/contributor_helper.rb#L16

We should add the joined deed type to this as well.

[benwbrum]

This has been fixed.