Improve the blob download/upload feature

1. [Getting the Page Ranges of a Large Page Blob in Segments](http://blogs.msdn.com/b/windowsazurestorage/archive/2012/03/26/getting-the-page-ranges-of-a-large-page-blob-in-segments.aspx)
2. Immediately fire user callback with error when one of batch operations failed
3. Speedsummary support instantly download/upload speed.
4. Fix typo and etc