my first commit

1. Using ErrorInfo class to handle error code and meassage .
When  caching  exceptions in the method of "downad()" , I get the
Meassges of the exception  and put it in a errorInfo ,then create a
DownloadThrowable that extends Throwable and contains the errorInfo.
2. In the class of DownloadManager ，I complete methods in the interface
of DownloadTaskListenner.
In the method of errorDownload ,I have  handled the queue of loadingtask
,the  cache of ConfigUitls and send broadcast .
When file is existing  i think it is not exception  it is  normal
process.
Revert "my first commit"

This reverts commit 0ff3c02c9afdc2826c42a81feec793d1e93b9d5b.
Revert "Revert "my first commit""

This reverts commit b2851a0e477b762adb0d69e499e95df6bea28a94.
Revert "my first commit"

This reverts commit 0ff3c02c9afdc2826c42a81feec793d1e93b9d5b.
Revert "Revert "my first commit""

This reverts commit 3bc39abfa9a2a201d98c7382b70916a0d046bc17.