Simple change to mastery calculations

Have it not punish you for sharing cs. Mastery grade should consider both the minions you killed, and the minions killed by nearby allies. This is important for 3 reasons: 1: ARAM 2: Games where it's tactically useful to let someone else waveclear. You're Annie and you want to hold onto your stun, so you let the gold-starved Sivir clear the wave from a safe distance rather than waste mana and cooldowns fighting with her for farm in the name of a chest. 3: Getting an S on support stops being a game of "build support items and then try to take as much cs as possible after laning to confuse the system".

This would greatly reduce the frustration of (and selfish things I do while) getting chests. So many situations where you're fed and snowballing, but you're melee and someone has good waveclear, so if you group and actually press the lead, no CS and no S. Easy thing to fix that'll make our own allies far less annoying.