Download to a temp directory, then apply all at once instead of one-by-one

[ManlyMarco]

There is a logic problem. KKManager delete old plugin first. At the same time download the new plugin. Here is the problem: if I spend many hours to download 7GB(mod pack) and several plugins failed to download (net problem, PC problem and etc.). the old mod cannot come back any more. Because of these missing mod and slowly download speed, I cannot play game for hours, days................ 0.9.3
Is it possible to add some protective mechanisms when the download fails.