invite to group link doesn't include enrollment token

[kapil1garg]

When a user receives an email for a group invitation, clicking the "Join Group" link should direct them to pairresearch.io to an enrollment or login page. However, the link currently directs to the home page.

Two cases to investigate:

1. User's account already exists, and they are being added to another group. In this case, they should be redirected to the login page or the groups page (pairresearch.io/groups) if already logged in.
2. User's account does not exist, and they should be register. In this case, they should be directed to the enrollment page.

[kapil1garg]

saw this happen with every person who signed up for DTR this cycle:

A current workaround is to use Forgot Password to get a password reset email (with link to set a new password), and then logging in after. The group the person was invited to will appear on their groups page then

[kapil1garg]

Reproduction steps:

• When running Pair Research locally, include the mail URL: MAIL_URL="<mail_url_here>" meteor run
• Try to add a member to a group. They should receive an email with a link (same as it does in production), and the link will also be shown in console (something like, Enrollment email URL: http://localhost:3000/#/enroll-account/SMJAdcuQt_RBxtD3IgITI5ndEeGN8wSOdsR1_R2wszV)