[Feature] Leave champion shards if each champion's mastery level is less than 7

[whqkdhfh13]

This is to allow the user to leave some shards for each champion if the user ever chooses to upgrade their champion mastery using the shard.

[chynonm]

This is the only feature I want for this program. An auto-sell option that leaves 3 shard for each unowned champion, 2 shards for mastery 5 or below, 1 shard for mastery 6 champions and sells all shards for mastery 7 champions. It takes forever currently to hop back in forth trying to figure out how much mastery each champion has and sell the appropriate amount manualy