Added more invitation stuff (#4027)

app/assets/stylesheets/application.bootstrap.scss

app/controllers/api/v1/admin/invitations_controller.rb

app/javascript/components/admin/manage_users/ManageUsers.jsx

...pt/components/admin/manage_users/forms/InviteUserForm.jsx

app/javascript/components/rooms/room/Room.jsx

app/javascript/helpers/forms/CreateInvitationHelpers.jsx

...ooks/mutations/admin/manage_users/useCreateInvitation.jsx

app/mailers/user_mailer.rb

app/views/user_mailer/invitation_email.html.erb

app/views/user_mailer/invitation_email.text.erb

config/routes.rb

public/locales/en.json

spec/controllers/admin/invitations_controller_spec.rb