Closes#766
- changes the on-disk representation from % to a multiplier,
eg 250 -> 2.5, as this is consistent with the other options
- resets deck configs at or below 1.3 to 2.5
- for any cards that were using a reset deck config, reset their
current factor if it's at or below 2.0x. The cutoff is arbitrary,
and just intended to make sure we catch cards the user has rated
Easy on multiple times. The existing due dates are left alone.
