Add a verification system

[dericksonmark]

Purpose

Add a verification system! Implements #98.

Approach

To verify their account, a member will need to:

1. Send !jira verify (MojiraBot will send them a 15 character token)
2. Comment on a specific Mojira ticket with their token
3. Send a private message to the bot with link <jira username>

The bot will check the ticket for their comment, and if the username and code matches, the accounts will be linked.

This also adds:

• A command !jira who or !jira whois to check the account linked to either a Mojira or a Discord account.
• A method to remove the verification role from a user temporarily, by reacting to the log message.
• A method to remove the verification link from a user, by reacting to the log message with ✂.

Future work

[dericksonmark]

I think this is as complete as I'm going to get it, so I am marking this pull request as ready for review.

[chandler05]

Looks like the team is in favor of adding this according to https://discord.com/channels/647810384031645728/647810521713606656/850795026674089985

[dericksonmark]

I've decided to close this for now. When creating this, I made many choices that are inefficient for the bot, like storing verifications in a Discord channel. After the jira.js and discord.js pull requests are merged, I plan to remake this in a more efficient way. :)