Per day counters for characters

[QuentinWidlocher]

As mentionned by this issue : #551
The per day counter doesn't work with characters (PC and NPC).
The OP used the description as a workaround but it would be nice to have the real counter, since it's directly editable from the selected character panel.

Playing a bit with monsters, it seems that text like (X/days) in action titles get parsed to create the counters, it would be perfect to replicate the same behavior with characters for things like spell slots.

WDYT ?