Custom message overlay

Build a custom overlay that allows us to customize and present to users when they log into the app.

Overlay should have a structure similar to the achievement overlay, with this format:

OK button and x button to dismiss.

Timing of messages:

- one time message... once it is dismissed, it is never seen again
- a one time message based on specific date or date range
- a 'forced' message - a critical message that can be turned on to be shown each time the user logs into the app, until admin turns it off.