Display recent session history

[pganssle]

Show the stats for at least the day's sessions, plus how many sessions have been completed in the current calendar day.

[pganssle]

This is partially completed in that have the statitistics modal, but I'd stilll like to see:

1. Confusion matrix per session
2. Statistics by day, week, etc, including confusion matrix.

I think the confusion matrix stuff will be more important in the "black chords" period (#8), since the progression involves adding inversions of the black chords selectively based on how the child is doing.