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. This addresses #16 very partially: the filename are still random, but some sort of file naming scheme could be devised (although BibDesk auto file will always be more powerful).
* 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.
* waits for arXiv to recreate PDFs for old articles if they are not anymore on cache. Happens a lot with arXiv mirrors.
* references the publication by id inside the AppleScript code, which means that multiple processes can run at the same time, without the danger of mixing the linked files between concurrently added publications.
* 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