Task request for Marshal, add registration system to the community

This is a task request for the Marshal bot in https://github.com/codename-littleboy/steemit-moderation Read the readme file to know more about what it does.

The task request is about adding registration system in the bot. The bot will register new users in a database. Here's what the bot must do:

• The bot will work normally and all its current functions will work properly.

• The bot will work on the registration channel in the text channels category and monitor the command !r and $register

• If someone posted any of these commands, the bot will reply (if the user is not registered):

You have requested to register your account. Please confirm your registration by sending 3 Steem to [steem account name] with the memo [randomly generated command memo]. Read the pinned messages for more information.

• If the user sends the correct memo with 3 steem, the bot will register that account.

• If wrong amount is sent, that is, less or more than 3 steem is sent, the bot will refund the sender with the message:

You sent the wrong amount.

• If a 3 steem transfer with wrong memo is sent, the bot will refund with the message:

Sorry, I couldn't recongnize the memo.

• If a user sends the !r or $register commands and the bot finds the author name already registered with a steem account in the database, it must return the following message:

[Discord user name], you are already registered with the steem account [steem account username]. Contact the Hive account@moderators for help.