Adding method writeTo to UploadedFile interface

This change allow users to simple copy uploaded files to their application, if needs. Applications that don't save files in the filesystem can use `getFile` method, that now throws an `IOException` to compliance with spec when we work with filesystem.

A new class was added, `CommonsUploadUploadedFile`. This class only delegates all operations to commons-fileupload API, allowing us to use methods like `write` that test if files can be moved, and if not, copy the file. This feature have a very good performance because moving files consumes less resources than copy to a new file, specially when copy too large files. I know this name is too uggly, but I can't think in another name. Ideas?

The `DefaultUploadedFile` class still exists to keep legacy code for users who overrides this class. I don't deprecated this class because can be reused in the future.

Targeted to 4.2 because changes public API, and adds new features.

Closes #881 and #882.
@lucascs Added a method to allow streams copy. 6a08ab2. I use a 4kb buffer to avoid too many system calls to write stream.