Implement number of hit indicators for UF and RoF

There is a small display bug with the initial cast of the spell,
but it updates quickly enough that it shouldn't be too noticeable
This still needs to be fixed though

Changed SendBuffDurationPacket to take a Buffs_Struct by reference
to allow more of the data to be obtained without more params

Added Client::SendBuffNumHitPacket(Buffs_Struct &buff, int slot)