Extract some variables into the DownloadResponse & Fix some issues fo…

[Locke93]

1. Refactor code: extract some variables into the download response `

• private int mResponseCode;
• private String mResponseMessage;
• private String mErrorMessage;
• private String mTransferEncoding;
• private long mContentLength;
• private long mRangeLength;
• private String mLocation; `

2. Fixed some issues for resumable download feature

• Fixed shouldn't add "Range" when request.isResumable() is false
• Fixed accessFile.seek shouldn't seek to cacheSize when request.isResumable() is false