Update front end files to working status with the database

With this PR, the extension is now working (if you manually add some text to the DB to test it)!!! :smile: 

This PR contains the migrations that update the database.
The announcement data are stored in the config_text table.
The user's status is stored in the user table as a simple boolean (1 shows ann... 0 if they closed it).

The logic for getting the announcement data and displaying it is all in the listener. I assume that by making this a much simpler example of an extension, this would be OK, as the logic is quite simple and will only be re-used once again, in the ACP.

Note: My idea for displaying announcements is simple: On installation, the user status bool is 0, so nothing shows. Any time an announcement is submitted in the ACP, all user status bools get switched to 1 so the announcement will show. When a user closes the announcement, the user's status bool goes back to 0 and they don't see it again, until the next time an announcement is submitted in the ACP, switching all bools back 1.
@EXreaction Should we be using the service_container here, or is it better to use the @config_text service here instead?