Add option to send personalised emails

[garg3133]

Earlier, we used to send personalised emails to everyone (a separate email to everyone with their email address in 'To:'), but that was changed in 8cf7c6d where we started sending a common email to everyone with their email addresses in 'Bcc:'. This was done for two reasons:

• It used to take a lot of time to send emails to everyone individually, and for that time period the browser used to keep on loading and it used to sometimes fail in between with no clear visibility of who has received the email and who has not.
• There is a limit on our email account on how many individual emails we can send out in 24 hrs duration.

But we still need a way to send personalised emails to our Alumni (a personalised email is where the email can contain some personal information of the recipient like their name).

And a second step that we need to take after this is to send the emails asynchronously instead of keeping the browser in "loading" state while the emails are being sent. This can be done by making use of message queues and corn jobs.