legs: make Y->C and C->F lists mutually exclusive

This fixes #2.

Signed-off-by: diditclear <didyourupgradeclear@gmail.com>
legs: remove standby input for now

We need separate stats for these. See #3.

Signed-off-by: diditclear <didyourupgradeclear@gmail.com>
legs.js: make sure Y->C is checked when selecting 3-class upgrade

This is to make sure the form displayed matches the value checked for "Type of upgrade?".

Signed-off-by: diditclear <didyourupgradeclear@gmail.com>