Refactor UploadedFile class to use composition.

Refactored teh UploadedFile class to use composition instead of
inheritance.  This should resolve issues with Symfony uploaded file
objects between v 2.3 (used by L4) and v 2.4 (used by L4.1).
Update unit tests.

Updated the test suite to ensure all tests are passing since recent
changes to the Codesleeve\Stapler\UploadedFile class were implemented.
Start writing tests for the UploadedFile class.

Started writing tests for the UploadedFile class.
Fix bug in UploadedFile class.

Fixed a bug in the UploadedFileClass that was being caused by a call to
the non-existent method 'getErrorCode' on the Symfony UploadedFile
class.
Merge branch 'development'