Add audio for numbers

[RuthTurk]

• Research how to add audio files to realm so that we can store the files similar to the rest of the data in the app. If that doesn't work, find a different way to store audio files.
• Add audio files for all the counting lessons so that a child can click on a button and hear how the number is pronounced. We will probably only have this option for French and Chadian Arabic, maybe English.