Apply the num factor when applying equipment capabilities

(Closes #3035)
(Closes #3020)
fix bugs in EquipSet:Count
fix incorrect counts in EquipSet:Add/Remove
fix iteration loop in EquipSet:Get

fixes #3039
fixes #3040
fix inconsistent parameter name in Ship:SetEquip
amend EquipSet:Set so it can remove items, and fix various bugs
update Ship:FireMissileAt to use new equipment methods and fix bugs

fixes #3038
fix InfoView/EconTrade view 'refuel full' button

fixes #3046
fix Player::Load to register its EquipSet change listener

This is necessary because the Ship's EquipSet object is replaced on Load
with a deserialised object from the Ship's propery map.