Blobs: Add static utility class for creating blobs (e.g. using blob parts)

[ShaunEdiger]

This convenience class enables the creation of Blob objects by wrapping the native Blob constructor in a GWT wrapper. Since blob parts are mixed javascript arrays, some Java type checking is performed on the Object arguments before passing them to the target JSNI method.

W3C Blob Interface: http://www.w3.org/TR/FileAPI/#dfn-Blob

[laaglu]

Looks pretty cool ! I will build it and try it asap