Integrated Editor for itmsp files

I am currently writing on a simple editor for `itmsp` files. Most of it already works, except of adding/removing locales. When a file is downloaded from ITC it will automatically be opened afterwards. You can already edit all of the meta data, easily add new screenshots and remove screenshots.

On the todolist/wishlist:
- Make locales list editable (remove/add locales)
- Reuse existing NSFileWrapper (don't rewrite screenshots, if no changes happened)
- Make the "Download from ITC" part its own window (shown when creating a new file)
- Make the verify/submit part its own window (shown when verify/submit is selected in the menu, while a document is open)
- Move ITC credentials into a separate settings window
- ~~Add a document icon~~ be91b16
- Support drag & drop for multiple screenshots at once, automatically assign correct device types
- Support drag & drop reordering of screenshots
- Visible Input validation (required fields, Max length. especially for keywords, screenshot size/format)

What do you think about it? Any chance for merging?

Screenshot:

![screenshot](https://f.cloud.github.com/assets/807039/2238716/f7c42a54-9bfd-11e3-9e02-71e9afe0872a.png)