R2LDanmaku:Reduce times of calucation
L2RDanmaku: Refactor
DrawTask: Clean up
DrawTask: Remove unused codes
CacheManagingDrawTask: Clean up
修复拖动进度后部分弹幕描边丢失问题
Optimize thread quit
CacheManagingDrawTask: Add a condition to findReuseableCache
Refactor & Add IDanmakuView