fix DanmakuIterator synchronized bug

java.util.ConcurrentModificationException
        at java.util.TreeMap$MapIterator.stepForward(TreeMap.java:883)
        at java.util.TreeMap$KeySet$1.next(TreeMap.java:959)
        at master.flame.danmaku.danmaku.model.android.Danmakus$DanmakuIterator.next(Unknown Source)
        at master.flame.danmaku.danmaku.renderer.android.DanmakusRetainer$RLDanmakusRetainer.fix(Unknown Source)
        at master.flame.danmaku.danmaku.renderer.android.DanmakusRetainer.fix(Unknown Source)
        at master.flame.danmaku.danmaku.renderer.android.DanmakuRenderer.draw(Unknown Source)
        at master.flame.danmaku.controller.DrawTask.drawDanmakus(Unknown Source)
        at master.flame.danmaku.controller.DrawTask.draw(Unknown Source)
        at master.flame.danmaku.controller.CacheManagingDrawTask.draw(Unknown Source)
        at master.flame.danmaku.controller.DrawHandler.draw(Unknown Source)
        at master.flame.danmaku.ui.widget.DanmakuSurfaceView.drawDanmakus(Unknown Source)
        at master.flame.danmaku.controller.DrawHandler.handleMessage(Unknown Source)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:194)
        at android.os.HandlerThread.run(HandlerThread.java:60)
Merge remote-tracking branch 'origin/master'

Conflicts:
	DanmakuFlameMaster/src/main/java/master/flame/danmaku/danmaku/model/android/Danmakus.java
revert Danmaku draw handler thread change in this commit