Recreate the Last Chance Cadet button mapping feature

[FrenjaminBanklin]

In Last Chance Cadet, it's possible to match left side to ride side by using the 123456 and qwerty keys. See below:

Reproduce this in the current Matching.

Also:

Last Chance Cadet does a better job of keeping track of which colors are currently in use, which Matching seems to be having some trouble with (i.e. sometimes there will be two matches on the same page using the same color).