Added "Heal" display to the window when looking at the staff for healing in the unit's possessions menu. Shows the amount of healing when using that staff.
This item is only displayed when selecting to Heal, Mend, Recover, Physic, or Fortify.
Even if the holder is unable to use that staff, the value that would be recovered if he/she were to use it will be displayed (handled in the same way as for other weapons).
