Update current 'work' branch to use appkit.

Hi Jonathan, and happy new year!

So, here's a major pull request that basically gets rid of every external AppleScript dependency and uses AppKit to do the work inside the python script. There are quite a few changes, so I'll let you digest and check if it suits you. I worked on the top of you most recent `work` branch.

Here are the major differences:

* no more injection of .applescript file - the `BibDesk` class handles the applescript calls via AppKit.
* no more `update_bibdesk_arxiv.sh` - you can go into `Pre-print Update mode` directly via `adsbibdesk -u [-f / -t]`.
* new `-o` option - this just downloads and opens the PDF (reader application can be changed in the preferences file). Nothing is added to `BibDesk`, it's just useful to check this or that reference without the need to go to arXiv and download PDFs by hand. I can provide a special Service for this if you wish.
* tries to find DOIs directly in the `strings` output of a PDF, if the `pdf2json` does not find anything - using this combination I was able to process 30% of my 650+ PDFs. It's not perfect though, since that for a couple of PDFs with lots of DOI URLs it returned everyone of them.
* uses ML Notification Center and falls back to Growl on other systems.
* strips directly the `<head></head>` of the ADS page - this is a different solution to issue #17, and IMHO its cleaner than cycling through and searching for the `<meta>` tags.
* adds the "ADS comment" (things like "14 pages, 14 figures, submitted response to ApJ referee comments on Dec 6, 2012") to the BibDesk entry
* miscellaneous cleanup

I also updated a bit the README files. I tested everything on Mountain Lion. There should be no problems neither in Lion. As for Snow Leopard, I can't test it, but the App *should* be compatible.

Cheers!
Rui