#2058 - Separate uploader logic into Kohana-, Item-Model-, and Uploadify-specific functions.
- Added _process_upload() to handle upload file validation with Kohana.
- Added _add_item() to handle item creation and validation with the item model (and logs).
- Removed these pieces from add_photo(), which is now rather Uploadify-specific.
- Used $_FILES to get filename instead of assuming it's substr(basename($tmp_name), 10).
- No net functional changes - works just like before.