contact/photo/set - Sets a new photo of a contact.

Method parameters:
id - The ID of the contact to set the photo of.
file - The photo file to upload.

Returns a JSON document of the following format:
<boolean> - Always true.

Expected errors:
CONTACT_NOT_FOUND - A contact with the ID doesn't exist.
SELECT_FILE - The photo file is empty.
INVALID_PHOTO - The photo couldn't be opened.
FILE_ERROR - An error occured while uploading the file.