Extend self-service event registration transfer to backend

When configuring an event, you have the option of enabling self-service cancel/transfer options for the registrant. This provides a link in the email and a link on the contact dashboard to cancel or transfer the registration.
To provide this transfer/cancel option to backend staff, here's the spec:
1. Add 'Transfer or Cancel' action against each event under contact record's Event tab. Clicking the action will open the participant's transfer/cancel form in a popup and rest will continue as per the existing workflow.
2. This action will be available to user with "edit event participants"
3. This action will also be available in Participant's view page.

IIDA-171