GSoC: Add support for Event Volunteer/Group/Membership in User/Admin Portal

[GlenDsza]

Is your feature request related to a problem? Please describe.
The Admin Portal & User Portal misses functionality of creating volunteers/ volunteer groups/inviting volunteers, etc.

Describe the solution you'd like
In Admin Portal (for Admin/Super Admin/Event Admin) in event Dashboard:

• Add support for CRUD of Event Volunteers (Individual)
• Add support for CRUD of Event Volunteer Groups, inviting members, etc.
• Assign Action Items to Volunteers

In User Portal,

• User should be able to view upcoming events, and available volunteer groups, join volunteer groups
• User should be able to accept/reject invitations for joining events & volunteer groups
• User should be able to view assigned action items.

Potential internship candidates

Please read this if you are planning to apply for a Palisadoes Foundation internship

• Student Internship Programs talawa#359