Notification System

## Summary
A system for SwadgePass and other modes to send text notifications to the player.

## Technical Spec
A notification will consist of 2 pointers: one to the name of the mode that created it, and one to the notification message. Messages must be fixed so that the mode doesn't need to be loaded to load the message.

The main menu will read the number of unread notifications and display an inbox-y icon.

Some reasonable limit on number of notifications (total and/or per mode) will need to be implemented.

## UI
1. Notification icon on the main menu with a number indicating how many notifications are unread
2. A screen for displaying notifications. Each notification will have a brief message and the name of the mode that sent it. When selected, the mode that sent the notification will be started.
3. Some way to clear notifications, either automatically when viewing them/opening the corresponding mode or manually per notification.

## Mockups
TBD

## How to Test
TBD