Ability for admin to subscribe any member of a chapter to a workshop

Description of the issue 📄

On the admin workshop view (admin/workshops/:id) admins have access to a dropdown that allows them to manually subscribe members of a chapter to any given workshop. Currently this dropdown is populated with members who have received but not accepted an invitation email. This is causing issues for the London chapter as we have stopped sending email invites for that chapter. Update this dropdown to show all members of a chapter who have not yet RSVP'd to the workshop.

Screenshots 📷

Dropdown to update

Steps to fix 🛠

Update the behaviour of the dropdown in the app/views/admin/workshops/_invitation_management.html.haml partial.

To do 📋

• Claim this issue (comment below, or assign yourself if you are part of the codebar org)
• Fork and clone the repository
• Update the relevant files. Follow the steps to fix section in this issue.
• Commit your changes as one commit. Use the title of this issue as your commit message
• Submit a pull request, make sure you mention #codebar24PR2017 in the description
• Mention this issue in the PR description by including it's number
• Have your pull request reviewed & merged by a codebar team member

Start in app/views/admin/workshops/_invitation_management.html.haml and inspect how the dropdown currently filters chapter members. Trace the existing invitation and RSVP data used there, then verify that members who have not RSVP'd appear regardless of invitation-email status. Done means the admin can select any non-RSVP'd chapter member for the workshop.