Add Event Announcements

Allow events to be registered into bot and announced on an announcement channel.

Changes Required:

• Have a simple event registration system for admins, include date, description, title and any other relevant info.
• Put storage in database for events, make it persistent. Events will have a flag that says closed/final once date is passed, set by trigger.
• Add commands for the above system.
• Add command to set an announcement channel where bot will make announcement based on configurable time limit (i.e. every day before event for x days).